mirror of
https://github.com/ceph/ceph
synced 2024-12-12 06:28:31 +00:00
120 lines
3.4 KiB
ReStructuredText
120 lines
3.4 KiB
ReStructuredText
============================
|
|
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. Choosing 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 CRUSH rule. For instance **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 CRUSH rule 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.
|
|
|
|
``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.
|
|
|