Adding upstream version 14.2.21.upstream/14.2.21upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 124 insertions, 0 deletions

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+.. _erasure-code-profiles:
+
+=====================
+Erasure code profiles
+=====================
+
+Erasure code is defined by a **profile** and is used when creating an
+erasure coded pool and the associated CRUSH rule.
+
+The **default** erasure code profile (which is created when the Ceph
+cluster is initialized) provides the same level of redundancy as two
+copies but requires 25% less disk space. It is described as a profile
+with **k=2** and **m=1**, meaning the information is spread over three
+OSD (k+m == 3) and one of them can be lost.
+
+To improve redundancy without increasing raw storage requirements, a
+new profile can be created. For instance, a profile with **k=10** and
+**m=4** can sustain the loss of four (**m=4**) OSDs by distributing an
+object on fourteen (k+m=14) OSDs. The object is first divided in
+**10** chunks (if the object is 10MB, each chunk is 1MB) and **4**
+coding chunks are computed, for recovery (each coding chunk has the
+same size as the data chunk, i.e. 1MB). The raw space overhead is only
+40% and the object will not be lost even if four OSDs break at the
+same time.
+
+.. _list of available plugins:
+
+.. toctree::
+	:maxdepth: 1
+
+	erasure-code-jerasure
+	erasure-code-isa
+	erasure-code-lrc
+	erasure-code-shec
+	erasure-code-clay
+
+osd erasure-code-profile set
+============================
+
+To create a new erasure code profile::
+
+	ceph osd erasure-code-profile set {name} \
+             [{directory=directory}] \
+             [{plugin=plugin}] \
+             [{stripe_unit=stripe_unit}] \
+             [{key=value} ...] \
+             [--force]
+
+Where:
+
+``{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
+
+``{plugin=plugin}``
+
+:Description: Use the erasure code **plugin** to compute coding chunks
+              and recover missing chunks. See the `list of available
+              plugins`_ for more information.
+
+:Type: String
+:Required: No.
+:Default: jerasure
+
+``{stripe_unit=stripe_unit}``
+
+:Description: The amount of data in a data chunk, per stripe. For
+              example, a profile with 2 data chunks and stripe_unit=4K
+              would put the range 0-4K in chunk 0, 4K-8K in chunk 1,
+              then 8K-12K in chunk 0 again. This should be a multiple
+              of 4K for best performance. The default value is taken
+              from the monitor config option
+              ``osd_pool_erasure_code_stripe_unit`` when a pool is
+              created.  The stripe_width of a pool using this profile
+              will be the number of data chunks multiplied by this
+              stripe_unit.
+
+:Type: String
+:Required: No.
+
+``{key=value}``
+
+:Description: The semantic of the remaining key/value pairs is defined
+              by the erasure code plugin.
+
+:Type: String
+:Required: No.
+
+``--force``
+
+:Description: Override an existing profile by the same name, and allow
+              setting a non-4K-aligned stripe_unit.
+
+:Type: String
+:Required: No.
+
+osd erasure-code-profile rm
+============================
+
+To remove an erasure code profile::
+
+	ceph osd erasure-code-profile rm {name}
+
+If the profile is referenced by a pool, the deletion will fail.
+
+osd erasure-code-profile get
+============================
+
+To display an erasure code profile::
+
+	ceph osd erasure-code-profile get {name}
+
+osd erasure-code-profile ls
+===========================
+
+To list the names of all erasure code profiles::
+
+	ceph osd erasure-code-profile ls
+