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-========================
-SHEC erasure code plugin
-========================
-
-The *shec* plugin encapsulates the `multiple SHEC
-<http://tracker.ceph.com/projects/ceph/wiki/Shingled_Erasure_Code_(SHEC)>`_
-library. It allows ceph to recover data more efficiently than Reed Solomon codes.
-
-Create an SHEC profile
-======================
-
-To create a new *shec* erasure code profile::
-
-        ceph osd erasure-code-profile set {name} \
-             plugin=shec \
-             [k={data-chunks}] \
-             [m={coding-chunks}] \
-             [c={durability-estimator}] \
-             [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: No.
-:Default: 4
-
-``m={coding-chunks}``
-
-:Description: Compute **coding-chunks** for each object and store them on
-              different OSDs. The number of **coding-chunks** does not necessarily
-              equal the number of OSDs that can be down without losing data.
-
-:Type: Integer
-:Required: No.
-:Default: 3
-
-``c={durability-estimator}``
-
-:Description: The number of parity chunks each of which includes each data chunk in its
-              calculation range. The number is used as a **durability estimator**.
-              For instance, if c=2, 2 OSDs can be down without losing data.
-
-:Type: Integer
-:Required: No.
-:Default: 2
-
-``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.
-
-Brief description of SHEC's layouts
-===================================
-
-Space Efficiency
-----------------
-
-Space efficiency is a ratio of data chunks to all ones in a object and
-represented as k/(k+m).
-In order to improve space efficiency, you should increase k or decrease m.
-
-::
-
-        space efficiency of SHEC(4,3,2) = 4/(4+3) = 0.57
-        SHEC(5,3,2) or SHEC(4,2,2) improves SHEC(4,3,2)'s space efficiency
-
-Durability
-----------
-
-The third parameter of SHEC (=c) is a durability estimator, which approximates
-the number of OSDs that can be down without losing data.
-
-``durability estimator of SHEC(4,3,2) = 2``
-
-Recovery Efficiency
--------------------
-
-Describing calculation of recovery efficiency is beyond the scope of this document,
-but at least increasing m without increasing c achieves improvement of recovery efficiency.
-(However, we must pay attention to the sacrifice of space efficiency in this case.)
-
-``SHEC(4,2,2) -> SHEC(4,3,2) : achieves improvement of recovery efficiency``
-
-Erasure code profile examples
-=============================
-
-::
-
-        $ ceph osd erasure-code-profile set SHECprofile \
-             plugin=shec \
-             k=8 m=4 c=3 \
-             crush-failure-domain=host
-        $ ceph osd pool create shecpool 256 256 erasure SHECprofile