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diff --git a/src/ceph/doc/rados/operations/erasure-code-shec.rst b/src/ceph/doc/rados/operations/erasure-code-shec.rst deleted file mode 100644 index e3bab37..0000000 --- a/src/ceph/doc/rados/operations/erasure-code-shec.rst +++ /dev/null @@ -1,144 +0,0 @@ -======================== -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 |