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============================
Jerasure erasure code plugin
============================
The *jerasure* plugin is the most generic and flexible plugin, it is
also the default for Ceph erasure coded pools.
The *jerasure* plugin encapsulates the `Jerasure
<http://jerasure.org>`_ library. It is
recommended to read the *jerasure* documentation to get a better
understanding of the parameters.
Create a jerasure profile
=========================
To create a new *jerasure* erasure code profile::
ceph osd erasure-code-profile set {name} \
plugin=jerasure \
k={data-chunks} \
m={coding-chunks} \
technique={reed_sol_van|reed_sol_r6_op|cauchy_orig|cauchy_good|liberation|blaum_roth|liber8tion} \
[crush-root={root}] \
[crush-failure-domain={bucket-type}] \
[crush-device-class={device-class}] \
[directory={directory}] \
[--force]
Where:
``k={data chunks}``
:Description: Each object is split in **data-chunks** parts,
each stored on a different OSD.
:Type: Integer
:Required: Yes.
:Example: 4
``m={coding-chunks}``
:Description: Compute **coding chunks** for each object and store them
on different OSDs. The number of coding chunks is also
the number of OSDs that can be down without losing data.
:Type: Integer
:Required: Yes.
:Example: 2
``technique={reed_sol_van|reed_sol_r6_op|cauchy_orig|cauchy_good|liberation|blaum_roth|liber8tion}``
:Description: The more flexible technique is *reed_sol_van* : it is
enough to set *k* and *m*. The *cauchy_good* technique
can be faster but you need to chose the *packetsize*
carefully. All of *reed_sol_r6_op*, *liberation*,
*blaum_roth*, *liber8tion* are *RAID6* equivalents in
the sense that they can only be configured with *m=2*.
:Type: String
:Required: No.
:Default: reed_sol_van
``packetsize={bytes}``
:Description: The encoding will be done on packets of *bytes* size at
a time. Chosing the right packet size is difficult. The
*jerasure* documentation contains extensive information
on this topic.
:Type: Integer
:Required: No.
:Default: 2048
``crush-root={root}``
:Description: The name of the crush bucket used for the first step of
the ruleset. For intance **step take default**.
:Type: String
:Required: No.
:Default: default
``crush-failure-domain={bucket-type}``
:Description: Ensure that no two chunks are in a bucket with the same
failure domain. For instance, if the failure domain is
**host** no two chunks will be stored on the same
host. It is used to create a ruleset step such as **step
chooseleaf host**.
:Type: String
:Required: No.
:Default: host
``crush-device-class={device-class}``
:Description: Restrict placement to devices of a specific class (e.g.,
``ssd`` or ``hdd``), using the crush device class names
in the CRUSH map.
:Type: String
:Required: No.
:Default:
``directory={directory}``
:Description: Set the **directory** name from which the erasure code
plugin is loaded.
:Type: String
:Required: No.
:Default: /usr/lib/ceph/erasure-code
``--force``
:Description: Override an existing profile by the same name.
:Type: String
:Required: No.
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