summaryrefslogtreecommitdiffstats
path: root/doc/rados/operations/erasure-code-jerasure.rst
diff options
context:
space:
mode:
Diffstat (limited to 'doc/rados/operations/erasure-code-jerasure.rst')
-rw-r--r--doc/rados/operations/erasure-code-jerasure.rst121
1 files changed, 121 insertions, 0 deletions
diff --git a/doc/rados/operations/erasure-code-jerasure.rst b/doc/rados/operations/erasure-code-jerasure.rst
new file mode 100644
index 000000000..553afa09d
--- /dev/null
+++ b/doc/rados/operations/erasure-code-jerasure.rst
@@ -0,0 +1,121 @@
+============================
+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:
+
+.. prompt:: bash $
+
+ 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.
+