ceph/man/crushtool.8

.TH "CRUSHTOOL" "8" "September 22, 2011" "dev" "Ceph"
.SH NAME
crushtool \- CRUSH map manipulation tool
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.SH SYNOPSIS
.nf
\fBcrushtool\fP ( \-d \fImap\fP | \-c \fImap.txt\fP | \-\-build \fInumosds\fP
\fIlayer1\fP \fI...\fP ) [ \-o \fIoutfile\fP [ \-\-clobber ]]
.fi
.sp
.SH DESCRIPTION
.sp
\fBcrushtool\fP is a utility that lets you create, compile, and
decompile CRUSH map files.
.sp
CRUSH is a pseudo\-random data distribution algorithm that efficiently
maps input values (typically data objects) across a heterogeneous,
hierarchically structured device map. The algorithm was originally
described in detail in the following paper (although it has evolved
some since then):
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.INDENT 3.5
\fI\%http://www.ssrc.ucsc.edu/Papers/weil-sc06.pdf\fP
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.sp
The tool has three modes of operation.
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.TP
.B \-c map.txt
will compile a plaintext map.txt into a binary map file.
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.TP
.B \-d map
will take the compiled map and decompile it into a plaintext source
file, suitable for editing.
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.TP
.B \-\-build numosds layer1 ...
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
.B \-o outfile
will specify the output file.
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.TP
.B \-\-clobber
will allow the tool to overwrite an existing outfile (it will normally refuse).
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.SH BUILDING A MAP
.sp
The build mode will generate relatively generic hierarchical maps. The
first argument simply specifies the number of devices (leaves) in the
CRUSH hierarchy. Each layer describes how the layer (or raw devices)
preceding it should be grouped.
.sp
Each layer consists of:
.sp
.nf
.ft C
name ( uniform | list | tree | straw ) size
.ft P
.fi
.sp
The first element is the name for the elements in the layer
(e.g. "rack"). Each element\(aqs name will be append a number to the
provided name.
.sp
The second component is the type of CRUSH bucket.
.sp
The third component is the maximum size of the bucket. If the size is
0, a single bucket will be generated that includes everything in the
preceding layer.
.SH EXAMPLE
.sp
Suppose we have 128 devices, each grouped into shelves with 4 devices
each, and 8 shelves per rack. We could create a three level hierarchy
with:
.sp
.nf
.ft C
crushtool \-\-build 128 shelf uniform 4 rack straw 8 root straw 0 \-o map
.ft P
.fi
.sp
To adjust the default (generic) mapping rules, we can run:
.sp
.nf
.ft C
# decompile
crushtool \-d map \-o map.txt

# edit
vi map.txt

# recompile
crushtool \-c map.txt \-o map
.ft P
.fi
.SH AVAILABILITY
.sp
\fBcrushtool\fP is part of the Ceph distributed file system. Please
refer to the Ceph wiki at \fI\%http://ceph.newdream.net/wiki\fP for more
information.
.SH SEE ALSO
.sp
\fBceph\fP(8),
\fBosdmaptool\fP(8),
\fBmkcephfs\fP(8)
.SH COPYRIGHT
2011, New Dream Network
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