CRUSHDIFF(8) Ceph CRUSHDIFF(8)

# [NAME](#NAME)

crushdiff - ceph crush map test tool

# [SYNOPSIS](#SYNOPSIS)

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

# [DESCRIPTION](#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), 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](#OPTIONS)

[**--compiled**](#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>**](#pg)

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

[**--osdmap <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**](#verbose)

Produce diagnostic output.

# [COMMANDS](#COMMANDS)

[**compare** *crushmap*](#compare)

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)

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

[**import** *crushmap*](#import)

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

# [EXAMPLE](#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](#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](#SEE_ALSO)

ceph <>(8), crushtool <>(8), osdmaptool <>(8),

# [Copyright](#Copyright)

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

October 24, 2026 dev

---

Document: crushdiff(8) from ceph-fips-19 19.2.7-r3 (Chainguard OS)
Source: https://github.com/ceph/ceph.git