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118 lines
2.8 KiB
ReStructuredText
118 lines
2.8 KiB
ReStructuredText
==========================================
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crushtool -- CRUSH map manipulation tool
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==========================================
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.. program:: crushtool
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Synopsis
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========
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| **crushtool** ( -d *map* | -c *map.txt* | --build *numosds*
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*layer1* *...* ) [ -o *outfile* [ --clobber ]]
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Description
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===========
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**crushtool** is a utility that lets you create, compile, and
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decompile CRUSH map files.
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CRUSH is a pseudo-random data distribution algorithm that efficiently
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maps input values (typically data objects) across a heterogeneous,
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hierarchically structured device map. The algorithm was originally
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described in detail in the following paper (although it has evolved
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some since then):
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http://www.ssrc.ucsc.edu/Papers/weil-sc06.pdf
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The tool has four modes of operation.
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.. option:: -c map.txt
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will compile a plaintext map.txt into a binary map file.
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.. option:: -d map
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will take the compiled map and decompile it into a plaintext source
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file, suitable for editing.
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.. option:: --build --num_osds {num-osds} layer1 ...
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will create a relatively generic map with the given layer
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structure. See below for examples.
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.. option:: --test ...
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will perform a dry run of a CRUSH mapping for a range of input object
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names, see crushtool --help for more information.
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Options
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=======
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.. option:: -o outfile
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will specify the output file.
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.. option:: --clobber
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will allow the tool to overwrite an existing outfile (it will normally refuse).
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Building a map
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==============
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The build mode will generate relatively generic hierarchical maps. The
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first argument simply specifies the number of devices (leaves) in the
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CRUSH hierarchy. Each layer describes how the layer (or raw devices)
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preceding it should be grouped.
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Each layer consists of::
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name ( uniform | list | tree | straw ) size
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The first element is the name for the elements in the layer
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(e.g. "rack"). Each element's name will be append a number to the
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provided name.
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The second component is the type of CRUSH bucket.
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The third component is the maximum size of the bucket. If the size is
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0, a single bucket will be generated that includes everything in the
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preceding layer.
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Example
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=======
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Suppose we have 128 devices, each grouped into shelves with 4 devices
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each, and 8 shelves per rack. We could create a three level hierarchy
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with::
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crushtool --build 128 shelf uniform 4 rack straw 8 root straw 0 -o map
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To adjust the default (generic) mapping rules, we can run::
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# decompile
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crushtool -d map -o map.txt
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# edit
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vi map.txt
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# recompile
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crushtool -c map.txt -o map
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Availability
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============
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**crushtool** is part of the Ceph distributed file system. Please
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refer to the Ceph documentation at http://ceph.com/docs for more
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information.
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See also
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========
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:doc:`ceph <ceph>`\(8),
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:doc:`osdmaptool <osdmaptool>`\(8),
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:doc:`mkcephfs <mkcephfs>`\(8)
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