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.TH "CRUSHDIFF" "8" "Oct 24, 2023" "dev" "Ceph"
.SH NAME
crushdiff \- ceph crush map test tool
.SH SYNOPSIS
.nf
\fBcrushdiff\fP [ \-\-osdmap \fIosdmap\fP ] [ \-\-pg\-dump \fIpg\-dump\fP ]
[ \-\-compiled ] [ \-\-verbose ] \fIcommand\fP \fIcrushmap\fP
.fi
.sp
.SH DESCRIPTION
.sp
\fBcrushdiff\fP is a utility that lets you test the effect of a crushmap
change: number of pgs, objects, bytes moved. This is a wrapper around
\fI\%osdmaptool\fP(8), relying on its \fB\-\-test\-map\-pgs\-dump\fP
option to get the list of changed pgs. Additionally it uses pg stats
to calculate the numbers of objects and bytes moved.
.sp
By default, \fBcrushdiff\fP will use the cluster current osdmap and pg
stats, which requires access to the cluster. Though one can use the
\fB\-\-osdmap\fP and \fB\-\-pg\-dump\fP options to test against previously
obtained data.
.SH OPTIONS
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.TP
.B \-\-compiled
The input/output crushmap is compiled. If the options is not
specified the expected/returned crushmap is in txt (decompiled)
format.
.UNINDENT
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.TP
.B \-\-pg\-dump <pg\-dump>
JSON output of \fBceph pg dump\fP\&. If not specified \fBcrushdiff\fP
will try to get data running the command itself.
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.TP
.B \-\-osdmap <osdmap>
The cluster osdmap, obtained with \fBceph osd getmap\fP command. If
not specified \fBcrushdiff\fP will try to get data running the
command itself.
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.TP
.B \-\-verbose
Produce diagnostic output.
.UNINDENT
.SH COMMANDS
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.TP
\fBcompare\fP \fIcrushmap\fP
Compare the crushmap from \fIcrushmap\fP 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.
.TP
\fBexport\fP \fIcrushmap\fP
Export crushmap to \fIcrushmap\fP file from the cluster osdmap.
.TP
\fBimport\fP \fIcrushmap\fP
Import crushmap from \fIcrushmap\fP file to the cluster osdmap.
.UNINDENT
.SH EXAMPLE
.sp
Get the current crushmap:
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.sp
.EX
crushdiff export cm.txt
.EE
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.sp
Edit the map:
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.EX
$EDITOR cm.txt
.EE
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.sp
Check the result:
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.EX
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
.EE
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.sp
When running with \fB\-\-verbose\fP option the output will also contain
detailed information about the affected pgs, like below:
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.EX
4.3     [0, 2, 1] \-> [1, 4, 2]
4.b     [0, 1, 3] \-> [2, 1, 3]
4.c     [4, 0, 1] \-> [4, 1, 2]
.EE
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.sp
i.e. a pg number, and its old and the new osd active sets.
.sp
If the result is satisfactory install the updated map:
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.sp
.EX
crushdiff import cm.txt
.EE
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.SH AVAILABILITY
.sp
\fBcrushdiff\fP is part of Ceph, a massively scalable, open\-source, distributed storage system.  Please
refer to the Ceph documentation at \fI\%https://docs.ceph.com\fP for more
information.
.SH SEE ALSO
.sp
\fI\%ceph\fP(8),
\fI\%crushtool\fP(8),
\fI\%osdmaptool\fP(8),
.SH COPYRIGHT
2010-2023, Inktank Storage, Inc. and contributors. Licensed under Creative Commons Attribution Share Alike 3.0 (CC-BY-SA-3.0)
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