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104 lines
2.6 KiB
ReStructuredText
104 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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erasure-code-shec
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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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