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CRUSHTOOL(8)			     Ceph			  CRUSHTOOL(8)

NAME
       crushtool - CRUSH map manipulation tool

SYNOPSIS
       crushtool ( -d map | -c map.txt | --build numosds
       layer1 ... ) [ -o outfile [ --clobber ]]

DESCRIPTION
       crushtool  is  a	 utility  that lets you create, compile, and decompile
       CRUSH map files.

       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):
	  http://www.ssrc.ucsc.edu/Papers/weil-sc06.pdf

       The tool has three modes of operation.

       -c map.txt
	      will compile a plaintext map.txt into a binary map file.

       -d map will take the compiled map and decompile	it  into  a  plaintext
	      source file, suitable for editing.

       --build numosds layer1 ...
	      will create a relatively generic map with the given layer struc‐
	      ture. See below for examples.

OPTIONS
       -o outfile
	      will specify the output file.

       --clobber
	      will allow the tool to overwrite an existing  outfile  (it  will
	      normally refuse).

BUILDING A MAP
       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.

       Each layer consists of:

       name ( uniform | list | tree | straw ) size

       The first element is the name for  the  elements	 in  the  layer	 (e.g.
       "rack").	 Each  element's  name will be append a number to the provided
       name.

       The second component is the type of CRUSH bucket.

       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.

EXAMPLE
       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:

       crushtool --build 128 shelf uniform 4 rack straw 8 root straw 0 -o map

       To adjust the default (generic) mapping rules, we can run:

       # decompile
       crushtool -d map -o map.txt

       # edit
       vi map.txt

       # recompile
       crushtool -c map.txt -o map

AVAILABILITY
       crushtool is part of the Ceph distributed file system. Please refer  to
       the Ceph wiki at http://ceph.newdream.net/wiki for more information.

SEE ALSO
       ceph(8), osdmaptool(8), mkcephfs(8)

COPYRIGHT
       2011, New Dream Network

dev			      September 22, 2011		  CRUSHTOOL(8)

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