---
name: "crushdiff"
section: "8"
platform: "linux"
package: "ceph-common"
version: "18.2.7+ds-1+deb13u1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/crushdiff"
---

# crushdiff(8)

ceph crush map test tool

## NAME

crushdiff - ceph crush map test tool

## SYNOPSIS

```
crushdiff [ --osdmap osdmap ] [ --pg-dump pg-dump ]
[ --compiled ] [ --verbose ] command crushmap
```

## DESCRIPTION

**crushdiff** is a utility that lets you test the effect of a crushmap change: number of pgs, objects, bytes moved. This is a wrapper around [*osdmaptool*(8)](/osdmaptool/8.md), relying on its **--test-map-pgs-dump** option to get the list of changed pgs. Additionally it uses pg stats to calculate the numbers of objects and bytes moved.

By default, **crushdiff** will use the cluster current osdmap and pg stats, which requires access to the cluster. Though one can use the **--osdmap** and **--pg-dump** options to test against previously obtained data.

## OPTIONS

- **--compiled**

  The input/output crushmap is compiled. If the options is not specified the expected/returned crushmap is in txt (decompiled) format.

- **--pg-dump \<pg-dump\>**

  JSON output of **ceph pg dump**. If not specified **crushdiff** will try to get data running the command itself.

- **--osdmap \<osdmap\>**

  The cluster osdmap, obtained with **ceph osd getmap** command. If not specified **crushdiff** will try to get data running the command itself.

- **--verbose**

  Produce diagnostic output.

## COMMANDS

- **compare** *crushmap*

  Compare the crushmap from *crushmap* file with the crushmap from the cluster osdmap. The output will show the expected number of pgs, objects, bytes moved when the new crushmap is installed.

- **export** *crushmap*

  Export crushmap to *crushmap* file from the cluster osdmap.

- **import** *crushmap*

  Import crushmap from *crushmap* file to the cluster osdmap.

## EXAMPLE

Get the current crushmap:

```
crushdiff export cm.txt
```

Edit the map:

```
$EDITOR cm.txt
```

Check the result:

```
crushdiff compare cm.txt
79/416 (18.99%) pgs affected
281/1392 (20.19%) objects affected
80/1248 (6.41%) pg shards to move
281/4176 (6.73%) pg object shards to move
730.52Mi/10.55Gi (6.76%) bytes to move
```

When running with **--verbose** option the output will also contain detailed information about the affected pgs, like below:

```
4.3     [0, 2, 1] -> [1, 4, 2]
4.b     [0, 1, 3] -> [2, 1, 3]
4.c     [4, 0, 1] -> [4, 1, 2]
```

i.e. a pg number, and its old and the new osd active sets.

If the result is satisfactory install the updated map:

```
crushdiff import cm.txt
```

## AVAILABILITY

**crushdiff** is part of Ceph, a massively scalable, open-source, distributed storage system.  Please refer to the Ceph documentation at *https://docs.ceph.com* for more information.

## SEE ALSO

[*ceph*(8)](/ceph/8.md), [*crushtool*(8)](/crushtool/8.md), [*osdmaptool*(8)](/osdmaptool/8.md),

## COPYRIGHT

2010-2014, Inktank Storage, Inc. and contributors. Licensed under Creative Commons Attribution Share Alike 3.0 (CC-BY-SA-3.0)