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https://github.com/ceph/ceph
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74 lines
2.6 KiB
Groff
74 lines
2.6 KiB
Groff
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.TH CRUSHTOOL 8
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.SH NAME
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crushtool \- CRUSH map manipulation tool
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.SH SYNOPSIS
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.B crushtool
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( \fB\-d\fI map\fP | \fB\-c\fI map.txt\fP | \fB\-\-build\fI numosds layer1 ...\fP )
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[ \fB\-o\fI outfile\fP [ \fB\-\-clobber\fP ]]
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.SH DESCRIPTION
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.B crushtool
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is a utility that lets you create, compile, and decompile CRUSH map files.
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.PP
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CRUSH is a pseudo-random data distribution algorithm that efficiently maps
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input values (typically data objects) across a heterogeneous, hierarchically
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structured device map. The algorithm was originally described in detail in
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the following paper (although it has evolved some since then):
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.IP
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http://www.ssrc.ucsc.edu/Papers/weil-sc06.pdf
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.PP
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The tool has three modes of operation.
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.TP
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\fB\-c\fI map.txt\fP
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will compile a plaintext \fImap.txt\fP into a binary map file.
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.TP
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\fB\-d\fI map\fP
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will take the compiled \fImap\fP and decompile it into a plaintext source file,
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suitable for editing.
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.TP
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\fB\-\-build\fI numosds layer1 ...\fP
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will create a relatively generic map with the given layer structure. See below for examples.
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.SH OPTIONS
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.TP
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\fB\-o\fI outfile\fP
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will specify the output file.
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.TP
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\fB\-\-clobber\fP
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will allow the tool to overwrite an existing \fIoutfile\fP (it will normally refuse).
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.SH BUILDING A MAP
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The build mode will generate relatively generic hierarchical maps. The first argument simply
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specifies the number of devices (leaves) in the CRUSH hierarchy. Each layer describes how the
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layer (or raw devices) preceeding it should be grouped.
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.PP
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Each \fIlayer\fP consists of
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.IP
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\fIname\fP ( uniform | list | tree | straw ) \fIsize\fP
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.PP
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The first element is the \fIname\fP for the elements in the layer (e.g. "rack"). Each element's
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name will be append a number to the provided \fIname\fP.
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.PP
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The second component is the type of CRUSH bucket.
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.PP
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The third component is the maximum size of the bucket. If the size is \fI0\fP, a single bucket
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will be generated that includes everything in the preceeding layer.
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.SH EXAMPLE
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Suppose we have 128 devices, each grouped into shelves with 4 devices each, and 8 shelves per
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rack. We could create a three level hierarchy with:
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.IP
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crushtool --build 128 shelf uniform 4 rack straw 8 root straw 0 -o map
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.PP
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To adjust the default (generic) mapping rules, we can
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.IP
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crushtool -d map -o map.txt # decompile
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.IP
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vi map.txt # edit
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.IP
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crushtool -c map.txt -o map # recompile
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.SH AVAILABILITY
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.B crushtool
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is part of the Ceph distributed file system. Please refer to the Ceph wiki at
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http://ceph.newdream.net/wiki for more information.
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.SH SEE ALSO
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.BR ceph (8),
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.BR osdmaptool (8),
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.BR mkcephfs (8)
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