This document is for a development version of Ceph.
crushdiff – ceph crush map test tool¶
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.
The input/output crushmap is compiled. If the options is not specified the expected/returned crushmap is in txt (decompiled) format.
JSON output of ceph pg dump. If not specified crushdiff will try to get data running the command itself.
The cluster osdmap, obtained with ceph osd getmap command. If not specified crushdiff will try to get data running the command itself.
Produce diagnostic output.
- 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.
Get the current crushmap:
crushdiff export cm.txt
Edit the map:
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
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.