crushtool - CRUSH map manipulation tool
crushtool ( -d map | -c map.txt | --build numosds layer1 ... ) [ -o
outfile [ --clobber ]]
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):
The tool has three modes of operation.
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
structure. See below for examples.
will specify the output file.
will allow the tool to overwrite an existing outfile (it will
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)
preceeding 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
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
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
crushtool --build 128 shelf uniform 4 rack straw 8 root straw 0
To adjust the default (generic) mapping rules, we can
crushtool -d map -o map.txt # decompile
vi map.txt # edit
crushtool -c map.txt -o map # recompile
crushtool is part of the Ceph distributed file system. Please refer to
the Ceph wiki at http://ceph.newdream.net/wiki for more information.
ceph(8), osdmaptool(8), mkcephfs(8)