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Merge pull request #48322 from zdover23/wip-doc-2022-10-01-rados-ops-ec-front-matter-rewrite

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doc/rados: rewrite EC intro

Reviewed-by: Cole Mitchell <cole.mitchell@gmail.com>
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zdover23 2022-10-01 14:32:10 +10:00 committed by GitHub
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doc/rados/operations/erasure-code.rst
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Erasure code
=============
A Ceph pool is associated to a type to sustain the loss of an OSD
(i.e. a disk since most of the time there is one OSD per disk). The
default choice when `creating a pool <../pools>`_ is *replicated*,
meaning every object is copied on multiple disks. The `Erasure Code
<https://en.wikipedia.org/wiki/Erasure_code>`_ pool type can be used
instead to save space.
By default, Ceph `pools <../pools>`_ are created with the type "replicated". In
replicated-type pools, every object is copied to multiple disks (this
multiple copying is the "replication").
In contrast, `erasure-coded <https://en.wikipedia.org/wiki/Erasure_code>`_
pools use a method of data protection that is different from replication. In
erasure coding, data is broken into fragments of two kinds: data blocks and
parity blocks. If a drive fails or becomes corrupted, the parity blocks are
used to rebuild the data. At scale, erasure coding saves space relative to
replication.
In this documentation, data blocks are referred to as "data chunks"
and parity blocks are referred to as "encoding chunks".
Erasure codes are also called "forward error correction codes". The
first forward error correction code was developed in 1950 by Richard
Hamming at Bell Laboratories.
Creating a sample erasure coded pool
------------------------------------