--- name: "multipath.conf" section: "5" platform: "linux" package: "multipath-tools" version: "0.15.1-1" release: "Arch Linux 2026-11-01" platforms: ["linux"] url: "https://new.carta.tech/multipath.conf" --- # multipath.conf(5) multipath daemon configuration file. ## NAME /etc/multipath.conf, /etc/multipath/conf.d/\*.conf - multipath daemon configuration file. ## DESCRIPTION **/etc/multipath.conf** is the configuration file for the multipath daemon. It is used to overwrite the built-in configuration table of **multipathd**. Any line whose first non-white-space character is a '#' is considered a comment line. Empty lines are ignored. Currently used multipathd configuration can be displayed with the **multipath -t** or **multipathd show config** command. Additional configuration can be made in drop-in files under **/etc/multipath/conf.d/**. Files ending in *.conf* in this directory are read in alphabetical order, after reading */etc/multipath.conf*. They use the same syntax as */etc/multipath.conf* itself, and support all sections and keywords. If a keyword occurs in the same section in multiple files, the last occurrence will take precedence over all others. ## SYNTAX The configuration file contains entries of the form: ```
{ ... { ... } } ``` Each *section* contains one or more attributes or subsections. The recognized keywords for attributes or subsections depend on the section in which they occur. **\** and **\** must be on a single line. **\** is one of the keywords listed in this man page. **\** is either a simple word (containing no whitespace and none of the characters '"', '#', and '!') or *one* string enclosed in double quotes ("..."). Outside a quoted string, text starting with '#', and '!' is regarded as a comment and ignored until the end of the line. Inside a quoted string, '#' and '!' are normal characters, and whitespace is preserved. To represent a double quote character inside a double quoted string, use two consecutive double quotes ('""'). Thus '2.5" SSD' can be written as "2.5"" SSD". Opening braces ('{') must follow the (sub)section name on the same line. Closing braces ('}') that mark the end of a (sub)section must be the only non-whitespace character on the line. Whitespace is ignored except inside double quotes, thus the indentation shown in the above example is helpful for human readers but not mandatory. **Note on regular expressions:** The */etc/multipath.conf* syntax allows many attribute values to be specified as POSIX Extended Regular Expressions (see [**regex**(7)](/regex/7.md)). These regular expressions are **case-sensitive** and **not anchored**, thus the expression "bar" matches "barbie", "rhabarber", and "wunderbar", but not "Barbie". To avoid unwanted substring matches, standard regular expression syntax using the special characters "^" and "$" can be used. The following *section* keywords are recognized: - **defaults** This section defines default values for attributes which are used whenever no values are given in the appropriate device or multipath sections. - **blacklist** This section defines which devices should be excluded from the multipath topology discovery. - **blacklist\_exceptions** This section defines which devices should be included in the multipath topology discovery, despite being listed in the *blacklist* section. - **multipaths** This section defines the multipath topologies. They are indexed by a *World Wide Identifier*(WWID). For details on the WWID generation see section *WWID generation* below. Attributes set in this section take precedence over all others. - **devices** This section defines the device-specific settings. Devices are identified by vendor, product, and revision. - **overrides** This section defines values for attributes that should override the device-specific settings for all devices. ## defaults section The *defaults* section recognizes the following keywords: - **verbosity** Default verbosity. Higher values increase the verbosity level. Valid levels are between 0 and 6. - The default is: **2** - **polling\_interval** Interval between two path checks in seconds. For properly functioning paths, the interval between checks will gradually increase to *max\_polling\_interval*. This value will be overridden by the *WatchdogSec* setting in the multipathd.service definition if systemd is used. - The default is: **5** - **max\_polling\_interval** Maximal interval between two path checks in seconds. - The default is: **4 \* polling\_interval** - **reassign\_maps** Enable reassigning of device-mapper maps. With this option multipathd will remap existing device-mapper maps to always point to multipath device, not the underlying block devices. Possible values are *yes* and *no*. - The default is: **no** - **multipath\_dir** (Deprecated) This option is not supported anymore, and will be ignored. - **path\_selector** The default path selector algorithm to use; they are offered by the kernel multipath target: - *round-robin 0* Choose the path for the next I/O request by **cycling through the path group**. - *queue-length 0* (Since 2.6.31 kernel) Choose the path for the next I/O request based on **the lowest** **number of outstanding in-flight I/O requests** to the path. - *service-time 0* (Since 2.6.31 kernel) Choose the path for the next I/O request based on **the** **lowest total size (in bytes) of outstanding in-flight I/O requests** to the path. - *historical-service-time 0* (Since 5.8 kernel) Choose the path for the next I/O request with **a dynamic** **algorithm based on the historical service time and the number of outstanding** **in-flight I/O requests** to the path. - The default is: **service-time 0** - **path\_grouping\_policy** (Hardware-dependent) The default path grouping policy to apply to unspecified multipaths. Possible values are: - *failover* One path per priority group. - *multibus* All paths in one priority group. - *group\_by\_serial* One priority group per serial number. - *group\_by\_prio* One priority group per priority value. Priorities are determined by callout programs specified as a global, per-controller or per-multipath option in the configuration file. - *group\_by\_node\_name* One priority group per target node name. Target node names are fetched in */sys/class/fc\_transport/target\*/node\_name*. - *group\_by\_tpg* One priority group per ALUA target port group. In order to use this policy, all paths in the multipath device must have *prio* set to **alua**. - The default is: **failover** - **detect\_pgpolicy** If set to *yes* and all path devices are configured with either the *alua* or *sysfs* prioritizer, the multipath device will automatically use the *group\_by\_prio* path\_grouping\_policy. If set to *no*, the path\_grouping\_policy will be selected as usual. - The default is: **yes** - **detect\_pgpolicy\_use\_tpg** If both this and *detect\_pgpolicy* are set to *yes* and all path devices are configured with either the *alua* or *sysfs* prioritizer, the multipath device will automatically use the *group\_by\_tpg* path\_grouping\_policy. If set to *no*, the path\_grouping\_policy will be selected by the method described for *detect\_pgpolicy* above. - The default is: **no** - **pg\_timeout** (Deprecated) This option is not supported anymore, and will be ignored. - **uid\_attrs** Setting this option activates **merging uevents** by WWID, which may improve uevent processing efficiency. Moreover, it's an alternative method to configure the udev properties to use for determining unique path identifiers (WWIDs). The value of this option is a space separated list of records like "*type:ATTR*", where *type* is matched against the beginning of the device node name (e.g. *sd:ATTR* matches *sda*), and *ATTR* is the name of the udev property to use for matching devices. If this option is configured and matches the device node name of a device, it overrides any other configured methods for determining the WWID for this device. This option cannot be changed during runtime with the multipathd **reconfigure** command. The default is: **\**. To enable uevent merging, set it e.g. to "sd:ID\_SERIAL dasd:ID\_UID nvme:ID\_WWN". - **uid\_attribute** The udev attribute providing a unique path identifier (WWID). If *uid\_attribute* is set to the empty string, WWID determination is done using the *sysfs* method rather than using udev (not recommended in production; see **WWID generation** below). - The default is: **ID\_SERIAL**, for SCSI devices - The default is: **ID\_UID**, for DASD devices - The default is: **ID\_WWN**, for NVMe devices - **getuid\_callout** (Deprecated) This option is not supported anymore, and will be ignored. - **prio** The name of the path priority routine. The specified routine should return a numeric value specifying the relative priority of this path. Higher number have a higher priority. *"none"* is a valid value. Currently the following path priority routines are implemented: - *const* Return a constant priority of *1*. - *sysfs* Use the sysfs attributes *access\_state* and *preferred\_path* to generate the path priority. This prioritizer accepts the optional prio\_arg *exclusive\_pref\_bit*. - *emc* (Hardware-dependent) Generate the path priority for DGC class arrays as CLARiiON CX/AX and EMC VNX families with Failover Mode 1 (Passive Not Ready(PNR)). - *alua* (Hardware-dependent) Generate the path priority based on the SCSI-3 ALUA settings. This prioritizer accepts the optional prio\_arg *exclusive\_pref\_bit*. - *ontap* (Hardware-dependent) Generate the path priority for NetApp ONTAP FAS/AFF Series and rebranded arrays, with ONTAP native mode(not ALUA). - *rdac* (Hardware-dependent) Generate the path priority for LSI/Engenio/NetApp RDAC class as NetApp SANtricity E/EF Series and rebranded arrays, with "Linux DM-MP (Kernel 3.9 or earlier)" option. - *hp\_sw* (Hardware-dependent) Generate the path priority for HP/COMPAQ/DEC HSG80 and MSA/HSV arrays with Active/Standby mode exclusively. - *hds* (Hardware-dependent) Generate the path priority for Hitachi AMS families of arrays other than AMS 2000. - *random* Generate a random priority between 1 and 10. - *weightedpath* Generate the path priority based on the regular expression and the priority provided as argument. Requires prio\_args keyword. - *path\_latency* Generate the path priority based on a latency algorithm. Requires prio\_args keyword. - *ana* (Hardware-dependent) Generate the path priority based on the NVMe ANA settings. - *datacore* (Hardware-dependent) Generate the path priority for some DataCore storage arrays. Requires prio\_args keyword. - *iet* (iSCSI only) Generate path priority for iSCSI targets based on IP address. Requires prio\_args keyword. The default depends on the **detect\_prio** setting: If **detect\_prio** is **yes** (default), the default priority algorithm is **sysfs** (except for NetAPP E/EF Series, where it is **alua**). If **detect\_prio** is **no**, the default priority algorithm is **const**. - **prio\_args** Arguments to pass to to the prio function. This only applies to certain prioritizers: - *weighted* Needs a value of the form *"\ \ \ \ \ ..."* - *hbtl* Regex can be of SCSI H:B:T:L format. For example: 1:0:.:. , \*:0:0:. - *devname* Regex can be of device name format. For example: sda , sd.e - *serial* Regex can be of serial number format. For example: .\*J1FR.\*324 . The serial can be looked up through sysfs or by running multipathd show paths format "%z". For example: 0395J1FR904324 - *wwn* Regex can be of the form *"host\_wwnn:host\_wwpn:target\_wwnn:target\_wwpn"* these values can be looked up through sysfs or by running *multipathd show paths format* *"%N:%R:%n:%r"*. For example: 0x200100e08ba0aea0:0x210100e08ba0aea0:.\*:.\* , .\*:.\*:iqn.2009-10.com.redhat.msp.lab.ask-06:.\* - *path\_latency* Needs a value of the form "io\_num=*\<20\>* base\_num=*\<10\>*" - *io\_num* The number of read IOs sent to the current path continuously, used to calculate the average path latency. Valid Values: Integer, \[20, 200\]. - *base\_num* The base number value of logarithmic scale, used to partition different priority ranks. Valid Values: Double-precision floating-point, \[1.1, 10\]. And Max average latency value is 100s, min average latency value is 1us. For example: If base\_num=10, the paths will be grouped in priority groups with path latency \<=1us, (1us, 10us\], (10us, 100us\], (100us, 1ms\], (1ms, 10ms\], (10ms, 100ms\], (100ms, 1s\], (1s, 10s\], (10s, 100s\], \>100s. - *alua* If *exclusive\_pref\_bit* is set, paths with the *preferred path* bit set will always be in their own path group. - *sysfs* If *exclusive\_pref\_bit* is set, paths with the *preferred path* bit set will always be in their own path group. - *datacore* - *preferredsds* (Mandatory) The preferred "SDS name". - *timeout* (Optional) The timeout for the INQUIRY, in ms. - *iet* - *preferredip=...* (Mandatory) The preferred IPv4 address, in dotted decimal notation, for iSCSI targets. It will be assigned priority 20 (high), while the rest will be assigned priority 0 (low). The value can also be a comma separated sequence of CIDR (IPv4 address/prefix) expressions, each followed by a colon and a priority. CIDR expressions can use standard *n.n.n.n/p* format or any valid shorthand, e.g. *192.168/16* as shorthand for *192.168.0.0/16*. IP addresses of iSCSI targets will be matched with each of these expressions. The most specific match (largest prefix) will be used to determine the priority. IP addresses that don't match any expression are assigned priority 0. Example: *10/8:20,10.0.10/24:40,192.168/16:10,0/0:5*. - The default is: **\** - **features** Specify any device-mapper features to be used. Syntax is *num list* where *num* is the number, between 0 and 8, of features in *list*. Possible values for the feature list are: - *queue\_if\_no\_path* (Deprecated, superseded by *no\_path\_retry*) Queue I/O if no path is active. Identical to the *no\_path\_retry* with *queue* value. If both this feature and *no\_path\_retry* are set, the latter value takes precedence. See KNOWN ISSUES. - *pg\_init\_retries \* (Since kernel 2.6.24) Number of times to retry pg\_init, it must be between 1 and 50. - *pg\_init\_delay\_msecs \* (Since kernel 2.6.38) Number of msecs before pg\_init retry, it must be between 0 and 60000. - *queue\_mode \* (Since kernel 4.8) Select the queueing mode per multipath device. \ can be *bio*, *rq* or *mq*, which corresponds to bio-based, request-based, and block-multiqueue (blk-mq) request-based, respectively. Before kernel 4.20 The default depends on the kernel parameter **dm\_mod.use\_blk\_mq**. It is *mq* if the latter is set, and *rq* otherwise. Since kernel 4.20, *rq* and *mq* both correspond to block-multiqueue. Once a multipath device has been created, its queue\_mode cannot be changed. *nvme:tcp* paths are only supported in multipath devices with queue\_mode set to *bio*. multipath will automatically set this when creating a device with *nvme:tcp* paths. - The default is: **0** - **path\_checker** The default method used to determine the path's state. Since multipath-tools 0.15.0, all path checkers run in asynchronous mode by default, so that unresponsive devices don't pause multipathd. Use the *force\_sync* parameter to enforce synchronous path checking instead. Possible values are: - *readsector0* (Deprecated) Read the first sector of the device. This checker is being deprecated, please use *tur* or *directio* instead. - *tur* (Hardware-dependent) Issue a *TEST UNIT READY* command to a SCSI device. - *emc\_clariion* (Hardware-dependent) Query the DGC/EMC specific EVPD page 0xC0 to determine the path state for CLARiiON CX/AX and EMC VNX and Unity arrays families. - *hp\_sw* (Hardware-dependent) Check the path state for HP/COMPAQ/DEC HSG80 and MSA/HSV arrays with Active/Standby mode exclusively. - *rdac* (Hardware-dependent) Check the path state for LSI/Engenio/NetApp RDAC class as NetApp SANtricity E/EF Series, and rebranded arrays. - *directio* Read the first sector with direct I/O. This checker could cause spurious path failures under high load. Increasing *checker\_timeout* can help with this. - *cciss\_tur* (Hardware-dependent) Check the path state for HP/COMPAQ Smart Array(CCISS) controllers. - *none* Do not check the device, fallback to use the values retrieved from sysfs - The default is: **tur** - **alias\_prefix** The *user\_friendly\_names* prefix. - The default is: **mpath** - **failback** Tell multipathd how to manage path group failback. To select *immediate* or a *value*, it's mandatory that the device has support for a working prioritizer. - *immediate* Immediately failback to the highest priority pathgroup that contains active paths. - *manual* Do not perform automatic failback. - *followover* Used to deal with multiple computers accessing the same Active/Passive storage devices. Only perform automatic failback when the first path of a pathgroup becomes active. This keeps a cluster node from automatically failing back when another node requested the failover. - *values \> 0* Deferred failback (time to defer in seconds). - The default is: **manual** - **rr\_min\_io** (Deprecated since kernel 4.6) This option is not supported anymore, and will be ignored. - **rr\_min\_io\_rq** (Deprecated since kernel 4.6) This option is not supported anymore, and will be ignored. - **max\_fds** Specify the maximum number of file descriptors that can be opened by multipath and multipathd. This is equivalent to ulimit -n. A value of *max* will set this to the system limit from */proc/sys/fs/nr\_open*. If this is not set, the maximum number of open file descriptors is taken from the calling process. It is usually 1024. To be safe, this should be set to the maximum number of paths plus 32, if that number is greater than 1024. - The default is: **max** - **rr\_weight** (Deprecated since kernel 4.6) This option is not supported anymore, and will be ignored. - **no\_path\_retry** Specify what to do when all paths are down. Possible values are: - *value \> 0* Number of retries until disable I/O queueing. - *fail* For immediate failure (no I/O queueing). - *queue* For never stop I/O queueing, similar to *queue\_if\_no\_path*. See KNOWN ISSUES. - The default is: **fail** - **queue\_without\_daemon** If set to *no* , when multipathd stops, queueing will be turned off for all devices. This is useful for devices that set no\_path\_retry. If a machine is shut down while all paths to a device are down, it is possible to hang waiting for I/O to return from the device after multipathd has been stopped. Without multipathd running, access to the paths cannot be restored, and the kernel cannot be told to stop queueing I/O. Setting queue\_without\_daemon to *no* , avoids this problem. - The default is: **no** - **checker\_timeout** Specify the timeout to use for path checkers and prioritizers, in seconds. Only prioritizers that issue scsi commands use checker\_timeout. If a path does not respond to the checker command after *checker\_timeout* seconds have elapsed, it is considered down. - The default is: in **/sys/block/\/device/timeout** - **allow\_usb\_devices** If set to *no* , all USB devices will be skipped during path discovery. If you intend to use multipath on USB attached devices, set this to *yes*. - The default is: **no** - **flush\_on\_last\_del** If set to *always* , multipathd will disable queueing when the last path to a device has been deleted. If set to *never* , multipathd will not disable queueing when the last path to a device has been deleted. Since multipath cannot safely remove a device while queueing is enabled, setting this to *never* means that multipathd will not automatically remove an unused multipath device whose paths are all deleted if it is currently set to queue\_if\_no\_path. If set to *unused* , multipathd will only disable queueing when the last path is removed if nothing currently has the multipath device or any of the kpartx partition devices on top of it open. - The default is: **unused** - **user\_friendly\_names** If set to *yes* , the bindings file */etc/multipath/bindings* is used to assign a persistent and unique alias to the multipath, in the form of *prefix*\ (where *prefix* is defined by *alias\_prefix*; by default *mpath*). If set to *no* , the WWID is used as the alias. In either case, this will be overridden by any specific aliases defined in the *multipaths* section. - The default is: **no** - **fast\_io\_fail\_tmo** Specify the number of seconds the SCSI layer will wait after a problem has been detected on a FC remote port before failing I/O to devices on that remote port. This should be smaller than dev\_loss\_tmo. Setting this to *off* will disable the timeout. - The default is: **5** - **dev\_loss\_tmo** Specify the number of seconds the SCSI layer will wait after a connection loss has been detected on a remote port before removing it from the system. This can be set to "infinity", which effectively means 136 years (2^32-1 seconds). This parameter is only applied to Fibre Channel and SAS devices. The value of *dev\_loss\_tmo* is restricted by other settings. If *fast\_io\_fail\_tmo* is set to a positive value, **multipathd** will make sure that the value of *dev\_loss\_tmo* is larger than *no\_path\_retry* \* *polling\_interval*. If *fast\_io\_fail\_tmo* is not set, the kernel limits the *dev\_loss\_tmo* value to 600 seconds. In this case, the user has to make sure that *no\_path\_retry* is smaller than *dev\_loss\_tmo / polling\_interval*. In particular, *no\_path\_retry* must not be set to "*queue*". See KNOWN ISSUES. When path devices reappear after a connection loss, it is much easier for the kernel to simply reactivate an inactive device than to re-add a previously deleted one. It is therefore recommended to set *dev\_loss\_tmo* to a large value within the restrictions mentioned above. Fibre Channel and SAS devices have hardware-dependent defaults, which are left unchanged if *dev\_loss\_tmo* is not specified. For a few storage arrays, the multipath-tools built-in settings override the default. Run *multipath -T* to see the settings for your device. - The default is: **\** - **eh\_deadline** Specify the maximum number of seconds the SCSI layer will spend doing error handling when scsi devices fail. After this timeout the scsi layer will perform a full HBA reset. Setting this may be necessary in cases where the rport is never lost, so *fast\_io\_fail\_tmo* and *dev\_loss\_tmo* will never trigger, but (frequently due to load) scsi commands still hang. **Note:** when the scsi error handler performs the HBA reset, all target paths on that HBA will be affected. eh\_deadline should only be set in cases where all targets on the affected HBAs are multipathed. - The default is: **\** - **max\_retries** Specify the maximum number of times the SCSI layer will retry IO commands for some types of SCSI errors before returning failure. Setting this can be helpful for cases where IO commands hang and timeout. By default, the SCSI layer will retry IOs 5 times. Reducing this value will allow multipath to retry the IO down another path sooner. Valid values are **0** through **5**. - The default is: **\** - **bindings\_file** (Deprecated) This option is not supported anymore, and will be ignored. - **wwids\_file** (Deprecated) This option is not supported anymore, and will be ignored. - **prkeys\_file** (Deprecated) This option is not supported anymore, and will be ignored. - **log\_checker\_err** If set to *once* , multipathd logs the first path checker error at logging level 2. Any later errors are logged at level 3 until the device is restored. If set to *always* , multipathd always logs the path checker error at logging level 2. - The default is: **always** - **reservation\_key** This is the service action reservation key used by mpathpersist. It must be set for all multipath devices using persistent reservations, and it must be the same as the RESERVATION KEY field of the PERSISTENT RESERVE OUT parameter list which contains an 8-byte value provided by the application client to the device server to identify the I\_T nexus. If the *--param-aptpl* option is used when registering the key with mpathpersist, **:aptpl** must be appended to the end of the reservation key. Alternatively, this can be set to **file**, which will store the RESERVATION KEY registered by mpathpersist in the */etc/multipath/prkeys* file. multipathd will then use this key to register additional paths as they appear. When the registration is removed, the RESERVATION KEY is removed from the */etc/multipath/prkeys* file. The prkeys file will automatically keep track of whether the key was registered with *--param-aptpl*. - The default is: **\** - **all\_tg\_pt** Set the 'all targets ports' flag when registering keys with mpathpersist. Some arrays automatically set and clear registration keys on all target ports from a host, instead of per target port per host. The ALL\_TG\_PT flag must be set to successfully use mpathpersist on these arrays. Setting this option is identical to calling mpathpersist with *--param-alltgpt* - The default is: **no** - **retain\_attached\_hw\_handler** (Obsolete for kernels \>= 4.3) If set to *yes* and the SCSI layer has already attached a hardware\_handler to the device, multipath will not force the device to use the hardware\_handler specified by /etc/multipath.conf. If the SCSI layer has not attached a hardware handler, multipath will continue to use its configured hardware handler. The default is: **yes** **Important Note:** Linux kernel 4.3 or newer always behaves as if **"retain\_attached\_hw\_handler yes"** was set. - **detect\_prio** If set to *yes* , multipath will try to detect if the device supports SCSI-3 ALUA. If so, the device will automatically use the *sysfs* prioritizer if the required sysfs attributes *access\_state* and *preferred\_path* are supported, or the *alua* prioritizer if not. If set to *no* , the prioritizer will be selected as usual. - The default is: **yes** - **detect\_checker** if set to *yes* , multipath will try to detect if the device supports SCSI-3 ALUA. If so, the device will automatically use the *tur* checker. If set to *no* , the checker will be selected as usual. - The default is: **yes** - **force\_sync** If set to *yes* , multipathd will call the path checkers in sync mode only. This means that only one checker will run at a time, and that multipathd may pause operating while it is waiting for a device to respond. This is useful in the case where many multipathd checkers running in parallel causes significant CPU pressure. - The default is: **no** - **strict\_timing** If set to *yes* , multipathd will start a new path checker loop after exactly one second, so that each path check will occur at exactly *polling\_interval* seconds. On busy systems path checks might take longer than one second; here the missing ticks will be accounted for on the next round. A warning will be printed if path checks take longer than *polling\_interval* seconds. - The default is: **no** - **deferred\_remove** If set to *yes* , multipathd will do a deferred remove instead of a regular remove when the last path device has been deleted. This means that if the multipath device is still in use, it will be freed when the last user closes it. If path is added to the multipath device before the last user closes it, the deferred remove will be canceled. - The default is: **no** - **partition\_delimiter** This parameter controls how multipath chooses the names of partition devices of multipath maps if a multipath map is renamed (e.g. if a map alias is added or changed). If this parameter is set to a string other than "/UNSET/" (even the empty string), multipath inserts that string between device name and partition number to construct the partition device name. Otherwise (i.e. if this parameter is unset or has the value "/UNSET/"), the behavior depends on the map name: if it ends in a digit, a *"p"* is inserted between name and partition number; otherwise, the partition number is simply appended. Distributions may use a non-null default value for this option; in this case, the user must set it to "/UNSET/" to obtain the original **\** behavior. Use *multipath -T* to check the current settings. - The default is: **\** - **config\_dir** (Deprecated) This option is not supported anymore, and will be ignored. - **san\_path\_err\_threshold** If set to a value greater than 0, multipathd will watch paths and check how many times a path has been failed due to errors.If the number of failures on a particular path is greater than the san\_path\_err\_threshold, then the path will not reinstate till san\_path\_err\_recovery\_time. These path failures should occur within a san\_path\_err\_forget\_rate checks, if not we will consider the path is good enough to reinstate. See "Shaky paths detection" below. - The default is: **no** - **san\_path\_err\_forget\_rate** If set to a value greater than 0, multipathd will check whether the path failures has exceeded the san\_path\_err\_threshold within this many checks i.e san\_path\_err\_forget\_rate . If so we will not reinstate the path till san\_path\_err\_recovery\_time. See "Shaky paths detection" below. - The default is: **no** - **san\_path\_err\_recovery\_time** If set to a value greater than 0, multipathd will make sure that when path failures has exceeded the san\_path\_err\_threshold within san\_path\_err\_forget\_rate then the path will be placed in failed state for san\_path\_err\_recovery\_time duration.Once san\_path\_err\_recovery\_time has timeout we will reinstate the failed path . san\_path\_err\_recovery\_time value should be in secs. See "Shaky paths detection" below. - The default is: **no** - **marginal\_path\_double\_failed\_time** One of the four parameters of supporting path check based on accounting IO error such as intermittent error. When a path failed event occurs twice in *marginal\_path\_double\_failed\_time* seconds due to an IO error and all the other three parameters are set, multipathd will fail the path and enqueue this path into a queue of which members are sent a couple of continuous direct reading asynchronous IOs at a fixed sample rate of 10HZ to start IO error accounting process. See "Shaky paths detection" below. - The default is: **no** - **marginal\_path\_err\_sample\_time** One of the four parameters of supporting path check based on accounting IO error such as intermittent error. If it is set to a value no less than 120, when a path fail event occurs twice in *marginal\_path\_double\_failed\_time* second due to an IO error, multipathd will fail the path and enqueue this path into a queue of which members are sent a couple of continuous direct reading asynchronous IOs at a fixed sample rate of 10HZ to start the IO accounting process for the path will last for *marginal\_path\_err\_sample\_time*. If the rate of IO error on a particular path is greater than the *marginal\_path\_err\_rate\_threshold*, then the path will not reinstate for *marginal\_path\_err\_recheck\_gap\_time* seconds unless there is only one active path. After *marginal\_path\_err\_recheck\_gap\_time* expires, the path will be requeued for rechecking. If checking result is good enough, the path will be reinstated. See "Shaky paths detection" below. - The default is: **no** - **marginal\_path\_err\_rate\_threshold** The error rate threshold as a permillage (1/1000). One of the four parameters of supporting path check based on accounting IO error such as intermittent error. Refer to *marginal\_path\_err\_sample\_time*. If the rate of IO errors on a particular path is greater than this parameter, then the path will not reinstate for *marginal\_path\_err\_recheck\_gap\_time* seconds unless there is only one active path. See "Shaky paths detection" below. - The default is: **no** - **marginal\_path\_err\_recheck\_gap\_time** One of the four parameters of supporting path check based on accounting IO error such as intermittent error. Refer to *marginal\_path\_err\_sample\_time*. If this parameter is set to a positive value, the failed path of which the IO error rate is larger than *marginal\_path\_err\_rate\_threshold* will be kept in failed state for *marginal\_path\_err\_recheck\_gap\_time* seconds. When *marginal\_path\_err\_recheck\_gap\_time* seconds expires, the path will be requeued for checking. If checking result is good enough, the path will be reinstated, or else it will keep failed. See "Shaky paths detection" below. - The default is: **no** - **delay\_watch\_checks** (Deprecated) This option is **deprecated**, and mapped to *san\_path\_err\_forget\_rate*. If this is set to a value greater than 0 and no *san\_path\_err* options are set, *san\_path\_err\_forget\_rate* will be set to the value of *delay\_watch\_checks* and *san\_path\_err\_threshold* will be set to 1. See the *san\_path\_err\_forget\_rate* and *san\_path\_err\_threshold* options, and "Shaky paths detection" below for more information. - The default is: **no** - **delay\_wait\_checks** (Deprecated) This option is **deprecated**, and mapped to *san\_path\_err\_recovery\_time*. If this is set to a value greater than 0 and no *san\_path\_err* options are set, *san\_path\_err\_recovery\_time* will be set to the value of *delay\_wait\_checks* times *max\_polling\_interval*. This will give approximately the same wait time as delay\_wait\_checks previously did. Also, *san\_path\_err\_threshold* will be set to 1. See the *san\_path\_err\_recovery\_time* and *san\_path\_err\_threshold* options, and "Shaky paths detection" below for more information. - The default is: **no** - **marginal\_pathgroups** If set to *off*, the *delay\_\*\_checks*, *marginal\_path\_\**, and *san\_path\_err\_\** options will keep marginal, or "shaky", paths from being reinstated until they have been monitored for some time. This can cause situations where all non-marginal paths are down, and no paths are usable until multipathd detects this and reinstates a marginal path. If the multipath device is not configured to queue IO in this case, it can cause IO errors to occur, even though there are marginal paths available. However, if this option is set to *on*, when one of the marginal path detecting methods determines that a path is marginal, it will be reinstated and placed in a separate pathgroup that will only be used after all the non-marginal pathgroups have been tried first. This prevents the possibility of IO errors occurring while marginal paths are still usable. After the path has been monitored for the configured time, and is declared healthy, it will be returned to its normal pathgroup. If this option is set to *fpin*, multipathd will receive fpin notifications, set path states to "marginal" accordingly, and regroup paths as described for *on*. This option can't be used in combination with other options for "Shaky path detection" (see below). **Note:** If this is set to *fpin*, the *marginal\_path\_\** and *san\_path\_err\_\** options are implicitly set to *no*. Also, this option cannot be switched either to or from *fpin* on a multipathd reconfigure. multipathd must be restarted for the change to take effect. See "Shaky paths detection" below for more information. - The default is: **off** - **find\_multipaths** This option controls whether multipath and multipathd try to create multipath maps over non-blacklisted devices they encounter. This matters a) when a device is encountered by **multipath -u** during udev rule processing (a device is blocked from further processing by higher layers - such as LVM - if and only if it´s considered a valid multipath device path), and b) when multipathd detects a new device. The following values are possible: - *strict* Both multipath and multipathd treat only such devices as multipath devices which have been part of a multipath map previously, and which are therefore listed in the */etc/multipath/wwids* file. Users can manually set up multipath maps using the **multipathd add map** command. Once set up manually, the map is remembered in the WWIDs file and will be set up automatically in the future. - *off* Multipath behaves like **strict**. Multipathd behaves like **greedy**. *no* or *0* is accepted as an alias for *off*. - *on* Both multipathd and multipath treat a device as multipath device if the conditions for **strict** are met, or if at least two non-blacklisted paths with the same WWID have been detected. *yes* or *1* is accepted as an alias for *on*. - *greedy* Both multipathd and multipath treat every non-blacklisted device as multipath device path. - *smart* This differs from *find\_multipaths on* only in the way it treats new devices for which only one path has been detected yet. When such a device is first encountered in udev rules, it is treated as a multipath device. multipathd waits whether additional paths with the same WWID appears. If that happens, it sets up a multipath map. If it doesn´t happen until a timeout expires, or if setting up the map fails, a new uevent is triggered for the device; at second encounter in the udev rules, the device will be treated as non-multipath and passed on to upper layers. **Note:** this may cause delays during device detection if there are single-path devices which aren´t blacklisted. - The default is: **strict** - **find\_multipaths\_timeout** Timeout, in seconds, to wait for additional paths after detecting the first one, if *find\_multipaths* *"smart"* (see above) is set. If the value is **positive**, this timeout is used for all unknown, non-blacklisted devices encountered. If the value is **negative** (recommended), it's only applied to "known" devices that have an entry in multipath's hardware table, either in the built-in table or in a *device* section; other ("unknown") devices will use a timeout of only 1 second to avoid booting delays. The value 0 means "use the built-in default". If *find\_multipath* has a value other than *smart*, this option has no effect. - The default is: **-10** (10s for known and 1s for unknown hardware) - **uxsock\_timeout** CLI receive timeout in milliseconds. For larger systems CLI commands might timeout before the multipathd lock is released and the CLI command can be processed. This will result in errors like "timeout receiving packet" to be returned from CLI commands. In these cases it is recommended to increase the CLI timeout to avoid those issues. - The default is: **4000** - **retrigger\_tries** Sets the number of times multipathd will try to retrigger a uevent to get the WWID. - The default is: **3** - **retrigger\_delay** Sets the amount of time, in seconds, to wait between retriggers. - The default is: **10** - **missing\_uev\_wait\_timeout** Controls how many seconds multipathd will wait, after a new multipath device is created, to receive a change event from udev for the device, before automatically enabling device reloads. Usually multipathd will delay reloads on a device until it receives a change uevent from the initial table load. - The default is: **30** - **skip\_kpartx** If set to *yes* , kpartx will not automatically create partitions on the device. - The default is: **no** - **purge\_disconnected** If set to *yes* , multipathd will automatically remove devices that are in a disconnected state. A path is considered disconnected when the TUR (Test Unit Ready) path checker receives the SCSI sense code "LOGICAL UNIT NOT SUPPORTED" (sense key 0x5, ASC/ASCQ 0x25/0x00). This typically indicates that the LUN has been unmapped or is no longer presented by the storage array. This option helps clean up stale device entries that would otherwise remain in the system. - The default is: **no** - **disable\_changed\_wwids** (Deprecated) This option is not supported anymore, and will be ignored. - **remove\_retries** This sets how may times multipath will retry removing a device that is in-use. Between each attempt, multipath will sleep 1 second. - The default is: **0** - **max\_sectors\_kb** Sets the *max\_sectors\_kb* device parameter on some path devices and the multipath device to the specified value. *max\_sectors\_kb* is the largest I/O size, in units of 1024 bytes, that the kernel allows for a single I/O request. For hardware devices like SCSI disks, this value is limited by the capabilities of the hardware. It is crucial that the value of a multipath map is never higher than the minimum value of of all its path devices. This is ensured by the kernel when a multipath map is loaded, but manipulating the values of a map or either of its paths while the map is live can cause race conditions and I/O errors. Therefore this value is only enforced by multipathd when a multipath map is first created, or when a path device is added to a map. In both cases, race conditions are avoided by the kernel. Setting *max\_sectors\_kb* does not guarantee that all path devices will have this value set. It is not an error if the value of a path device is higher than that of the containing multipath map. It is also not an error if the actual limit of a map is lower than the value in */etc/multipath.conf*. This can happen if the hardware limits of one or more path devices are lower than the configured value. Normally the kernel and its device drivers take care of the maximum I/O size, and administrators do not need to bother about *max\_sectors\_kb*. But some hardware devices may report incorrect I/O size limits, or other components in the environment (e.g. the fabric) may impose constraints that the kernel cannot detect. In such cases setting *max\_sectors\_kb* makes sense. It should be set when maps are first created, and not be changed thereafter. If the setting **must** be changed for a live map, set the value in */etc/multipath.conf*, run **multipathd reconfigure**, and use **multipathd del path \** and **multipathd add path \** to delete and re-add the same path device. The default is: **\** - **ghost\_delay** Sets the number of seconds that multipath will wait after creating a device with only ghost paths before marking it ready for use in systemd. This gives the active paths time to appear before the multipath runs the hardware handler to switch the ghost paths to active ones. Setting this to *0* or *no* makes multipath immediately mark a device with only ghost paths as ready. - The default is: **no** - **auto\_resize** Controls when multipathd will automatically resize a multipath device. If set to *never*, multipath devices must always be manually resized by either running **multipathd resize map \**. If set to *grow\_only*, when multipathd detects that all of a multipath device's paths have increased in size, it will automatically grow the multipath device to the new size. If set to *grow\_shrink*, multipathd will also automatically shrink the device once it detects all of its paths have decreased in size. - The default is: **never** - **enable\_foreign** Enables or disables foreign libraries (see section *FOREIGN MULTIPATH SUPPORT* below). The value is a regular expression; foreign libraries are loaded if their name (e.g. "nvme") matches the expression. By default, no foreign libraries are enabled. Set this to "nvme" to enable NVMe native multipath support, or ".\*" to enable all foreign libraries. - The default is: **"NONE"** - **recheck\_wwid** If set to *yes*, when a failed path is restored, its wwid is rechecked. If the wwid has changed, the path is removed from the current multipath device, and re-added as a new path. Multipathd will also recheck a path's wwid if it is manually re-added. This option only works for SCSI devices that are configured to use the default uid\_attribute, *ID\_SERIAL*, or sysfs for getting their wwid. - The default is: **no** ## blacklist and blacklist\_exceptions sections The *blacklist* section is used to exclude specific devices from the multipath topology. It is most commonly used to exclude local disks or non-disk devices (such as LUNs for the storage array controller) from being handled by multipath-tools. In the *blacklist* and *blacklist\_exceptions* sections, starting a quoted value with an exclamation mark **"!"** will invert the matching of the rest of the regular expression. For instance, **"!^sd\[a-z\]"** will match all values that do not start with **"sd\[a-z\]"**. The exclamation mark can be escaped **"\\!"** to match a literal **!** at the start of a regular expression. **Note:** The exclamation mark must be inside quotes, otherwise it will be treated as starting a comment. The *blacklist\_exceptions* section is used to revert the actions of the *blacklist* section. This allows one to selectively include ("whitelist") devices which would normally be excluded via the *blacklist* section. A common usage is to blacklist "everything" using a catch-all regular expression, and create specific blacklist\_exceptions entries for those devices that should be handled by multipath-tools. The following keywords are recognized in both sections. The defaults are empty unless explicitly stated. - **devnode** Regular expression matching the device nodes to be excluded/included. The default *blacklist* consists of the regular expression **"!^(sd\[a-z\]\|dasd\[a-z\]\|nvme\[0-9\])"**. This causes all device types other than scsi, dasd, and nvme to be excluded from multipath handling by default. - **wwid** Regular expression for the *World Wide Identifier* of a device to be excluded/included. - **device** Subsection for the device description. This subsection recognizes the **vendor** and **product** keywords. Both are regular expressions. For a full description of these keywords please see the *devices* section description. - **property** Regular expression for an udev property. All devices that have matching udev properties will be excluded/included. The handling of the *property* keyword is special, because devices **must** have at least one whitelisted udev property; otherwise they're treated as blacklisted, and the message "*blacklisted, udev property missing*" is displayed in the logs. **Note:** The behavior of this option has changed in **multipath-tools** 0.8.2 compared to previous versions. Blacklisting by missing properties is only applied to devices which do have the property specified by *uid\_attribute* (e.g. *ID\_SERIAL*) set. Previously, it was applied to every device, possibly causing devices to be blacklisted because of temporary I/O error conditions. The default *blacklist exception* is: **(SCSI\_IDENT\_\|ID\_WWN)**, causing well-behaved SCSI devices and devices that provide a WWN (World Wide Number) to be included, and all others to be excluded. - **protocol** Regular expression for the protocol of a device to be excluded/included. The protocol strings that multipath recognizes are *scsi:fcp*, *scsi:spi*, *scsi:ssa*, *scsi:sbp*, *scsi:srp*, *scsi:iscsi*, *scsi:sas*, *scsi:adt*, *scsi:ata*, *scsi:unspec*, *nvme:pcie*, *nvme:rdma*, *nvme:fc*, *nvme:tcp*, *nvme:loop*, *nvme:apple-nvme*, *nvme:unspec*, *ccw*, *cciss*, and *undef*. The protocol that a path is using can be viewed by running **multipathd show paths format "%d %P"** For every device, these 5 blacklist criteria are evaluated in the order "property, devnode, device, protocol, wwid". If a device turns out to be blacklisted by any criterion, it's excluded from handling by multipathd, and the later criteria aren't evaluated anymore. For each criterion, the whitelist takes precedence over the blacklist if a device matches both. **Note:** Besides the blacklist and whitelist, other configuration options such as *find\_multipaths* have an impact on whether or not a given device is handled by multipath-tools. ## multipaths section The *multipaths* section allows setting attributes of multipath maps. The attributes that are set via the multipaths section (see list below) take precedence over all other configuration settings, including those from the *overrides* section. The only recognized attribute for the *multipaths* section is the *multipath* subsection. If there are multiple *multipath* subsections matching a given WWID, the contents of these sections are merged, and settings from later entries take precedence. The *multipath* subsection recognizes the following attributes: - **wwid** (Mandatory) World Wide Identifier. Detected multipath maps are matched against this attribute. Note that, unlike the *wwid* attribute in the *blacklist* section, this is **not** a regular expression or a substring; WWIDs must match exactly inside the multipaths section. - **alias** Symbolic name for the multipath map. This takes precedence over an entry for the same WWID in the */etc/multipath/bindings* file. The following attributes are optional; if not set the default values are taken from the *overrides*, *devices*, or *defaults* section: - **path\_grouping\_policy** - **path\_selector** - **prio** - **prio\_args** - **failback** - **no\_path\_retry** - **flush\_on\_last\_del** - **features** - **reservation\_key** - **user\_friendly\_names** - **deferred\_remove** - **san\_path\_err\_threshold** - **san\_path\_err\_forget\_rate** - **san\_path\_err\_recovery\_time** - **marginal\_path\_err\_sample\_time** - **marginal\_path\_err\_rate\_threshold** - **marginal\_path\_err\_recheck\_gap\_time** - **marginal\_path\_double\_failed\_time** - **delay\_watch\_checks** - **delay\_wait\_checks** - **skip\_kpartx** - **purge\_disconnected** - **max\_sectors\_kb** - **ghost\_delay** ## devices section - **Important:** The built-in hardware device table of *multipath-tools* is created by members of the Linux community in the hope that it will be useful. The existence of an entry for a given storage product in the hardware table **does not imply** that the product vendor supports, or has tested, the product with *multipath-tools* in any way. **Always consult the vendor's official documentation for support-related information.** *multipath-tools* have a built-in device table with reasonable defaults for more than 100 known multipath-capable storage devices. The devices section can be used to override these settings. If there are multiple matches for a given device, the attributes of all matching entries are applied to it. If an attribute is specified in several matching device subsections, later entries take precedence. Thus, entries in files under the */etc/multipath/conf.d/* directory (in reverse alphabetical order) have the highest precedence, followed by entries in */etc/multipath.conf*; the built-in hardware table has the lowest precedence. Inside a configuration file, later entries have higher precedence than earlier ones. The only recognized attribute for the *devices* section is the *device* subsection. Devices detected in the system are matched against the device entries using the **vendor**, **product**, and **revision** fields, which are all POSIX Extended regular expressions (see [**regex**(7)](/regex/7.md)). The vendor, product, and revision fields that multipath or multipathd detect for devices in a system depend on the device type. For SCSI devices, they correspond to the respective fields of the SCSI INQUIRY page. In general, the command '*multipathd show* *paths format "%d %s"*' command can be used to see the detected properties for all devices in the system. The *device* subsection recognizes the following attributes: - **vendor** (Mandatory) Regular expression to match the vendor name. - For DASD devices, it is the fixed label: **IBM** - For NVMe devices, it is the fixed label: **NVME** - **product** (Mandatory) Regular expression to match the product name. - For DASD devices, it is the fixed label: **S/390 DASD ECKD** - **revision** Regular expression to match the product revision. If not specified, any revision matches. - **product\_blacklist** Products with the given **vendor** matching this string are blacklisted. This is equivalent to a **device** entry in the *blacklist* section with the *vendor* attribute set to this entry's *vendor*, and the *product* attribute set to the value of *product\_blacklist*. - **alias\_prefix** The user\_friendly\_names prefix to use for this device type, instead of the default "mpath". - **vpd\_vendor** The vendor specific vpd page information, using the vpd page abbreviation. The vpd page abbreviation can be found by running *sg\_vpd -e*. multipathd will use this information to gather device specific information that can be displayed with the *%g* wildcard for the *multipathd show maps format* and *multipathd show paths format* commands. Currently only the **hp3par** vpd page is supported. - **hardware\_handler** The hardware handler to use for this device type. The following hardware handler are implemented: - *1 emc* (Hardware-dependent) Hardware handler for DGC class arrays as CLARiiON CX/AX and EMC VNX families with Failover Mode 1 (Passive Not Ready(PNR)). - *1 rdac* (Hardware-dependent) Hardware handler for LSI/Engenio/NetApp RDAC class as NetApp SANtricity E/EF Series and rebranded arrays, with "Linux DM-MP (Kernel 3.9 or earlier)" option. - *1 hp\_sw* (Hardware-dependent) Hardware handler for HP/COMPAQ/DEC HSG80 and MSA/HSV arrays with Active/Standby mode exclusively. - *1 alua* (Hardware-dependent) Hardware handler for SCSI-3 ALUA compatible arrays. - *1 ana* (Hardware-dependent) Hardware handler for NVMe ANA compatible arrays. The default is: **\** **Important Note:** Linux kernels 4.3 and newer automatically attach a device handler to known devices (which includes all devices supporting SCSI-3 ALUA) and disallow changing the handler afterwards. Setting **hardware\_handler** for such devices on these kernels has no effect. The following attributes are optional; if not set the default values are taken from the *defaults* section: - **path\_grouping\_policy** - **uid\_attribute** - **path\_selector** - **path\_checker** - **prio** - **prio\_args** - **features** - **failback** - **no\_path\_retry** - **fast\_io\_fail\_tmo** - **dev\_loss\_tmo** - **eh\_deadline** - **flush\_on\_last\_del** - **user\_friendly\_names** - **retain\_attached\_hw\_handler** - **detect\_prio** - **detect\_checker** - **deferred\_remove** - **san\_path\_err\_threshold** - **san\_path\_err\_forget\_rate** - **san\_path\_err\_recovery\_time** - **marginal\_path\_err\_sample\_time** - **marginal\_path\_err\_rate\_threshold** - **marginal\_path\_err\_recheck\_gap\_time** - **marginal\_path\_double\_failed\_time** - **delay\_watch\_checks** - **delay\_wait\_checks** - **skip\_kpartx** - **purge\_disconnected** - **max\_sectors\_kb** - **ghost\_delay** - **all\_tg\_pt** ## overrides section The overrides section recognizes the following optional attributes; if not set the values are taken from the *devices* or *defaults* sections: - **path\_grouping\_policy** - **uid\_attribute** - **path\_selector** - **path\_checker** - **alias\_prefix** - **features** - **prio** - **prio\_args** - **failback** - **no\_path\_retry** - **flush\_on\_last\_del** - **fast\_io\_fail\_tmo** - **dev\_loss\_tmo** - **eh\_deadline** - **user\_friendly\_names** - **retain\_attached\_hw\_handler** - **detect\_prio** - **detect\_checker** - **deferred\_remove** - **san\_path\_err\_threshold** - **san\_path\_err\_forget\_rate** - **san\_path\_err\_recovery\_time** - **marginal\_path\_err\_sample\_time** - **marginal\_path\_err\_rate\_threshold** - **marginal\_path\_err\_recheck\_gap\_time** - **marginal\_path\_double\_failed\_time** - **delay\_watch\_checks** - **delay\_wait\_checks** - **skip\_kpartx** - **purge\_disconnected** - **max\_sectors\_kb** - **ghost\_delay** - **all\_tg\_pt** The overrides section also recognizes the optional *protocol* subsection, and can contain multiple protocol subsections. Path devices are matched against the protocol subsection using the mandatory *type* attribute. Attributes in a matching protocol subsection take precedence over attributes in the rest of the overrides section. If there are multiple matching protocol subsections, later entries take precedence. - **protocol subsection** The protocol subsection recognizes the following mandatory attribute: - **type** The protocol string of the path device. The possible values are *scsi:fcp*, *scsi:spi*, *scsi:ssa*, *scsi:sbp*, *scsi:srp*, *scsi:iscsi*, *scsi:sas*, *scsi:adt*, *scsi:ata*, *scsi:unspec*, *nvme:pcie*, *nvme:rdma*, *nvme:fc*, *nvme:tcp*, *nvme:loop*, *nvme:apple-nvme*, *nvme:unspec*, *ccw*, *cciss*, and *undef*. This is **not** a regular expression. the path device protocol string must match exactly. The protocol that a path is using can be viewed by running **multipathd show paths format "%d %P"** The following attributes are optional; if not set, the default values are taken from the *overrides*, *devices*, or *defaults* section: - **fast\_io\_fail\_tmo** - **dev\_loss\_tmo** - **eh\_deadline** ## WWID generation Multipath uses a *World Wide Identification* (WWID) to determine which paths belong to the same device. Each path presenting the same WWID is assumed to point to the same device. The WWID is generated by four methods (in the order of preference): - **uid\_attrs** The WWID is derived from udev attributes by matching the device node name; cf *uid\_attrs* above. - **uid\_attribute** Use the value of the specified udev attribute; cf *uid\_attribute* above. - **sysfs** Try to determine the WWID from sysfs attributes. For SCSI devices, this means reading the Vital Product Data (VPD) page "Device Identification" (0x83). The default settings (using udev and **uid\_attribute** configured from the built-in hardware table) should work fine in most scenarios. Users who want to enable uevent merging must set **uid\_attrs**. ## Shaky paths detection A common problem in SAN setups is the occurrence of intermittent errors: a path is unreachable, then reachable again for a short time, disappears again, and so forth. This happens typically on unstable interconnects. It is undesirable to switch pathgroups unnecessarily on such frequent, unreliable events. *multipathd* supports three different methods for detecting this situation and dealing with it. All methods share the same basic mode of operation: If a path is found to be "shaky" or "flipping", and appears to be in healthy status, it is not reinstated (put back to use) immediately. Instead, it is placed in the "delayed" state and watched for some time, and only reinstated if the healthy state appears to be stable. If the *marginal\_pathgroups* option is set, the path will reinstated immediately, but placed in a special pathgroup for marginal paths. Marginal pathgroups will not be used until all other pathgroups have been tried. At the time when the path would normally be reinstated, it will be returned to its normal pathgroup. The logic of determining "shaky" condition, as well as the logic when to reinstate, differs between the three methods. - **"delay\_checks" failure tracking** (Deprecated) This method is **deprecated** and mapped to the "san\_path\_err" method. See the *delay\_watch\_checks* and *delay\_wait\_checks* options above for more information. - **"marginal\_path" failure tracking** If a second failure event (good-\>bad transition) occurs within *marginal\_path\_double\_failed\_time* seconds after a failure, high-frequency monitoring is started for the affected path: I/O is sent at a rate of 10 per second. This is done for *marginal\_path\_err\_sample\_time* seconds. During this period, the path is not reinstated. If the rate of errors remains below *marginal\_path\_err\_rate\_threshold* during the monitoring period, the path is reinstated. Otherwise, it is kept in failed state for *marginal\_path\_err\_recheck\_gap\_time*, and after that, it is monitored again. For this method, time intervals are measured in seconds. - **"san\_path\_err" failure tracking** multipathd counts path failures for each path. Once the number of failures exceeds the value given by *san\_path\_err\_threshold*, the path is not reinstated for *san\_path\_err\_recovery\_time* seconds. While counting failures, multipathd "forgets" one past failure every "san\_path\_err\_forget\_rate" ticks; thus if errors don't occur more often then once in the forget rate interval, the failure count doesn't increase and the threshold is never reached. Ticks are the time between path checks by multipathd, which is variable and controlled by the *polling\_interval* and *max\_polling\_interval* parameters. This algorithm is superseded by the "marginal\_path" failure tracking, but remains supported for backward compatibility. - **"FPIN" failure tracking** Fibre channel fabrics can notify hosts about fabric-level issues such as integrity failures or congestion with so-called Fabric Performance Impact Notifications (FPINs).On receiving the fpin notifications through ELS multipathd will move the affected path and port states to marginal. See the documentation of the individual options above for details. It is **strongly discouraged** to use more than one of these methods for any given multipath map, because the two concurrent methods may interact in unpredictable ways. If the "marginal\_path" method is active, the "san\_path\_err" parameters are implicitly set to 0. ## FOREIGN MULTIPATH SUPPORT multipath and multipathd can load "foreign" libraries to add support for other multipathing technologies besides the Linux device mapper. Currently this support is limited to printing detected information about multipath setup. In topology output, the names of foreign maps are prefixed by the foreign library name in square brackets, as in this example: ``` # multipath -ll uuid.fedcba98-3579-4567-8765-123456789abc [nvme]:nvme4n9 NVME,Some NVMe controller,FFFFFFFF size=167772160 features='n/a' hwhandler='ANA' wp=rw |-+- policy='n/a' prio=50 status=optimized | `- 4:38:1 nvme4c38n1 0:0 n/a optimized live `-+- policy='n/a' prio=50 status=optimized `- 4:39:1 nvme4c39n1 0:0 n/a optimized live ``` The "nvme" foreign library provides support for NVMe native multipathing in the kernel. It is part of the standard multipath package. ## KNOWN ISSUES The usage of *queue\_if\_no\_path* option can lead to *D state* processes being hung and not killable in situations where all the paths to the LUN go offline. It is advisable to use the *no\_path\_retry* option instead. The use of *queue\_if\_no\_path* or *no\_path\_retry* might lead to a deadlock if the *dev\_loss\_tmo* setting results in a device being removed while I/O is still queued. The multipath daemon will update the *dev\_loss\_tmo* setting accordingly to avoid this deadlock. Hence if both values are specified the order of precedence is *no\_path\_retry, queue\_if\_no\_path, dev\_loss\_tmo*. ## FILES Default paths for configuration files and directories: - */etc/multipath.conf* Main configuration file. - */etc/multipath/conf.d/* Directory for configuration drop-in files. - */etc/multipath/bindings* Bindings file, used when the **user\_friendly\_names** option is set to **yes** to assign a persistent and unique alias to each multipath device. - */etc/multipath/prkeys* Persistent reservation keys file, used by multipathd to keep track of the reservation key used for a specific WWID when **reservation\_key** is set to **file**. - */etc/multipath/wwids* WWIDs file, used by multipath to keep track of the WWIDs of LUNs for which multipath devices have been created in the past. - */run/multipathd.pid* PID file. ## SEE ALSO [**udev**(8)](/udev/8.md), [**dmsetup**(8)](/dmsetup/8.md), [**multipath**(8)](/multipath/8.md), [**multipathc**(8)](/multipathc/8.md), [**multipathd**(8)](/multipathd/8.md). ## AUTHORS *multipath-tools* was developed by Christophe Varoqui, \ and others.