---
name: "mhddfs"
section: "1"
platform: "linux"
package: "mhddfs"
version: "0.1.39+nmu2"
release: "Debian 12 (Bookworm)"
platforms: ["linux"]
url: "https://new.carta.tech/mhddfs"
---

# mhddfs(1)

The driver combines a several mount points into the single one.

## NAME

mhddfs - The driver combines a several mount points into the single one.

## SYNOPSIS

 mhddfs /dir1,/dir2\[,/path/to/dir3\] /path/to/mount \[-o options\]\
  mhddfs /dir1 dir2,dir3 /mount/point \[-o options\]\
  ...\
  fusermount -u /path/to/mount

### fstab record example:

mhddfs#/path/to/dir1,/path/to/dir2 /mnt/point fuse defaults 0 0

mhddfs#/dir1,/dir2,/dir3 /mnt fuse logfile=/var/log/mhddfs.log 0 0

## OPTIONS

with an  **-o option1,option2...** you can specify some additional options:

### logfile=/path/to/file.log

specify a file that will contain debug information.

### loglevel=x

0 - debug messages

1 - info messages

2 - standard (default) messages

### mlimit=size\[m\|k\|g\]

a free space size threshold If a drive has the free space less than the threshold specifed then another drive will be choosen while creating a new file.  If all the drives have free space less than the threshold specified then a drive containing most free space will be choosen.

Default value is 4G, minimum value is 100M.

This option accepts suffixes:

\[mM\] - megabytes

\[gG\] - gigabytes

\[kK\] - kilobytes

For an information about the additional options see output of:

**mhddfs -h**

## DESCRIPTION

The file system allows to unite a several mount points (or directories) to the single one. So a one big filesystem is simulated and this makes it possible to combine a several hard drives or network file systems. This system is like **unionfs** but it can choose a drive with the most of free space, and move the data between drives transparently for the applications.

While writing files they are written to a 1st hdd until the hdd has the free space (see mlimit option), then they are written on a 2nd hdd, then to 3rd etc.

**df** will show a total statistics of all filesystems like there is a big one hdd.

If an overflow arises while writing to the hdd1 then a file content already written will be transferred to a hdd containing enough of free space for a file. The transferring is processed on-the-fly, fully transparent for the application that is writing. So this behaviour simulates a big file system.

### WARNINGS

The filesystems are combined must provide a possibility to get their parameters correctly (e.g. size of free space). Otherwise the writing failure can occur (but data consistency will be ok anyway). For example it is a bad idea to combine a several  **sshfs** systems together.

Please read FUSE documentation for a further conception.

## COPYRIGHT

Distributed under  **GPLv3**

Copyright (C) 2008 Dmitry E. Oboukhov  *\<dimka@avanto.org\>*