.TH "CRUSHTOOL" "8" "November 18, 2013" "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 \-\-num_osds \fInumosds\fP
\fIlayer1\fP \fI...\fP ) [ \-o \fIoutfile\fP ]
.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):
.INDENT 0.0
.INDENT 3.5
\fI\%http://www.ssrc.ucsc.edu/Papers/weil-sc06.pdf\fP
.UNINDENT
.UNINDENT
.sp
The tool has four modes of operation.
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.TP
.B \-c map.txt
will compile a plaintext map.txt into a binary map file.
.UNINDENT
.INDENT 0.0
.TP
.B \-d map
will take the compiled map and decompile it into a plaintext source
file, suitable for editing.
.UNINDENT
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.TP
.B \-\-build \-\-num_osds {num\-osds} layer1 ...
will create a relatively generic map with the given layer
structure. See below for examples.
.UNINDENT
.INDENT 0.0
.TP
.B \-\-test
will perform a dry run of a CRUSH mapping for a range of input object
names, see crushtool \-\-help for more information.
.UNINDENT
.SH OPTIONS
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.TP
.B \-o outfile
will specify the output file.
.UNINDENT
.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 two rows with two racks each and 20 nodes per rack. Suppose
each node contains 4 storage devices for Ceph OSD Daemons. This configuration
allows us to deploy 320 Ceph OSD Daemons. Lets assume a 42U rack with 2U nodes,
leaving an extra 2U for a rack switch.
.sp
To reflect our hierarchy of devices, nodes, racks and rows, we would execute
the following:
.sp
.nf
.ft C
crushtool \-o crushmap \-\-build \-\-num_osds 320 node straw 4 rack straw 20 row straw 2
.ft P
.fi
.sp
To adjust the default (generic) mapping rules, we can run:
.sp
.nf
.ft C
# decompile
crushtool \-d crushmap \-o map.txt

# edit
vi map.txt

# recompile
crushtool \-c map.txt \-o crushmap
.ft P
.fi
.SH AVAILABILITY
.sp
\fBcrushtool\fP is part of the Ceph distributed file system. Please
refer to the Ceph documentation at \fI\%http://ceph.com/docs\fP for more
information.
.SH SEE ALSO
.sp
\fBceph\fP(8),
\fBosdmaptool\fP(8),
.SH COPYRIGHT
2010-2013, Inktank Storage, Inc. and contributors. Licensed under Creative Commons BY-SA
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