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Since kraken, Ceph enforces a 1:1 correspondence between CRUSH ruleset and CRUSH rule, so effectively ruleset and rule are the same thing, although the term "ruleset" still survives - notably in the CRUSH rule itself, where it effectively denotes the number of the rule. This commit updates the documentation to more faithfully reflect the current state of the code. Fixes: http://tracker.ceph.com/issues/20559 Signed-off-by: Nathan Cutler <ncutler@suse.com>
121 lines
3.4 KiB
ReStructuredText
121 lines
3.4 KiB
ReStructuredText
============================
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Jerasure erasure code plugin
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============================
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The *jerasure* plugin is the most generic and flexible plugin, it is
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also the default for Ceph erasure coded pools.
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The *jerasure* plugin encapsulates the `Jerasure
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<http://jerasure.org>`_ library. It is
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recommended to read the *jerasure* documentation to get a better
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understanding of the parameters.
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Create a jerasure profile
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=========================
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To create a new *jerasure* erasure code profile::
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ceph osd erasure-code-profile set {name} \
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plugin=jerasure \
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k={data-chunks} \
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m={coding-chunks} \
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technique={reed_sol_van|reed_sol_r6_op|cauchy_orig|cauchy_good|liberation|blaum_roth|liber8tion} \
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[crush-root={root}] \
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[crush-failure-domain={bucket-type}] \
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[crush-device-class={device-class}] \
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[directory={directory}] \
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[--force]
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Where:
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``k={data chunks}``
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:Description: Each object is split in **data-chunks** parts,
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each stored on a different OSD.
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:Type: Integer
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:Required: Yes.
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:Example: 4
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``m={coding-chunks}``
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:Description: Compute **coding chunks** for each object and store them
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on different OSDs. The number of coding chunks is also
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the number of OSDs that can be down without losing data.
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:Type: Integer
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:Required: Yes.
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:Example: 2
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``technique={reed_sol_van|reed_sol_r6_op|cauchy_orig|cauchy_good|liberation|blaum_roth|liber8tion}``
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:Description: The more flexible technique is *reed_sol_van* : it is
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enough to set *k* and *m*. The *cauchy_good* technique
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can be faster but you need to chose the *packetsize*
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carefully. All of *reed_sol_r6_op*, *liberation*,
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*blaum_roth*, *liber8tion* are *RAID6* equivalents in
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the sense that they can only be configured with *m=2*.
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:Type: String
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:Required: No.
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:Default: reed_sol_van
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``packetsize={bytes}``
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:Description: The encoding will be done on packets of *bytes* size at
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a time. Chosing the right packet size is difficult. The
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*jerasure* documentation contains extensive information
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on this topic.
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:Type: Integer
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:Required: No.
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:Default: 2048
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``crush-root={root}``
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:Description: The name of the crush bucket used for the first step of
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the CRUSH rule. For intance **step take default**.
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:Type: String
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:Required: No.
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:Default: default
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``crush-failure-domain={bucket-type}``
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:Description: Ensure that no two chunks are in a bucket with the same
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failure domain. For instance, if the failure domain is
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**host** no two chunks will be stored on the same
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host. It is used to create a CRUSH rule step such as **step
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chooseleaf host**.
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:Type: String
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:Required: No.
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:Default: host
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``crush-device-class={device-class}``
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:Description: Restrict placement to devices of a specific class (e.g.,
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``ssd`` or ``hdd``), using the crush device class names
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in the CRUSH map.
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:Type: String
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:Required: No.
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:Default:
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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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``--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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