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The plugins are made a sub-section of the erasure code profile section. The k and m parameters are removed from erasure code profile documentation. They were added for simplicity in the first version because there was only one plugin. But they should really be in the plugin documentation. Signed-off-by: Loic Dachary <loic-201408@dachary.org>
103 lines
2.6 KiB
ReStructuredText
103 lines
2.6 KiB
ReStructuredText
=====================
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Erasure code profiles
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=====================
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Erasure code is defined by a **profile** and is used when creating an
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erasure coded pool and the associated crush ruleset.
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The **default** erasure code profile (which is created when the Ceph
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cluster is initialized) provides the same level of redundancy as two
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copies but requires 25% less disk space. It is described as a profile
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with **k=2** and **m=1**, meaning the information is spread over three
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OSD (k+m == 3) and one of them can be lost.
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To improve redundancy without increasing raw storage requirements, a
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new profile can be created. For instance, a profile with **k=10** and
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**m=4** can sustain the loss of four (**m=4**) OSDs by distributing an
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object on fourteen (k+m=14) OSDs. The object is first divided in
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**10** chunks (if the object is 10MB, each chunk is 1MB) and **4**
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coding chunks are computed, for recovery (each coding chunk has the
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same size as the data chunk, i.e. 1MB). The raw space overhead is only
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40% and the object will not be lost even if four OSDs break at the
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same time.
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.. _list of available plugins:
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.. toctree::
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:maxdepth: 1
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erasure-code-jerasure
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erasure-code-isa
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erasure-code-lrc
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osd erasure-code-profile set
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============================
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To create a new erasure code profile::
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ceph osd erasure-code-profile set {name} \
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[{directory=directory}] \
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[{plugin=plugin}] \
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[{key=value} ...] \
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[--force]
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Where:
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``{directory=directory}``
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:Description: Set the **directory** name from which the erasure code
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plugin is loaded.
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:Type: String
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:Required: No.
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:Default: /usr/lib/ceph/erasure-code
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``{plugin=plugin}``
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:Description: Use the erasure code **plugin** to compute coding chunks
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and recover missing chunks. See the `list of available
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plugins`_ for more information.
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:Type: String
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:Required: No.
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:Default: jerasure
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``{key=value}``
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:Description: The semantic of the remaining key/value pairs is defined
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by the erasure code plugin.
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:Type: String
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:Required: No.
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``--force``
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:Description: Override an existing profile by the same name.
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:Type: String
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:Required: No.
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osd erasure-code-profile rm
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============================
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To remove an erasure code profile::
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ceph osd erasure-code-profile rm {name}
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If the profile is referenced by a pool, the deletion will fail.
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osd erasure-code-profile get
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============================
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To display an erasure code profile::
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ceph osd erasure-code-profile get {name}
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osd erasure-code-profile ls
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===========================
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To list the names of all erasure code profiles::
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ceph osd erasure-code-profile ls
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