From e1616a9985cad24284d324410422688264913101 Mon Sep 17 00:00:00 2001 From: Zac Dover Date: Fri, 2 Sep 2022 05:08:00 +1000 Subject: [PATCH] doc/rados: rewrite EC intro This PR rewrites the front matter in the "Erasure Code" section of the RADOS documentation. Previously, the information in this section was syntactically confused. I have also fleshed out the distinction between erasure coding and replication. Co-Author: Cole Mitchell Signed-off-by: Zac Dover --- doc/rados/operations/erasure-code.rst | 24 ++++++++++++++++++------ 1 file changed, 18 insertions(+), 6 deletions(-) diff --git a/doc/rados/operations/erasure-code.rst b/doc/rados/operations/erasure-code.rst index ddbea214ba5d..44473841121b 100644 --- a/doc/rados/operations/erasure-code.rst +++ b/doc/rados/operations/erasure-code.rst @@ -4,12 +4,24 @@ 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 -`_ 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 `_ +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 ------------------------------------ -- 2.47.3