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diff --git a/src/ceph/doc/dev/osd_internals/erasure_coding.rst b/src/ceph/doc/dev/osd_internals/erasure_coding.rst deleted file mode 100644 index 7263cc3..0000000 --- a/src/ceph/doc/dev/osd_internals/erasure_coding.rst +++ /dev/null @@ -1,82 +0,0 @@ -============================== -Erasure Coded Placement Groups -============================== - -Glossary --------- - -*chunk* - when the encoding function is called, it returns chunks of the same - size. Data chunks which can be concatenated to reconstruct the original - object and coding chunks which can be used to rebuild a lost chunk. - -*chunk rank* - the index of a chunk when returned by the encoding function. The - rank of the first chunk is 0, the rank of the second chunk is 1 - etc. - -*stripe* - when an object is too large to be encoded with a single call, - each set of chunks created by a call to the encoding function is - called a stripe. - -*shard|strip* - an ordered sequence of chunks of the same rank from the same - object. For a given placement group, each OSD contains shards of - the same rank. When dealing with objects that are encoded with a - single operation, *chunk* is sometime used instead of *shard* - because the shard is made of a single chunk. The *chunks* in a - *shard* are ordered according to the rank of the stripe they belong - to. - -*K* - the number of data *chunks*, i.e. the number of *chunks* in which the - original object is divided. For instance if *K* = 2 a 10KB object - will be divided into *K* objects of 5KB each. - -*M* - the number of coding *chunks*, i.e. the number of additional *chunks* - computed by the encoding functions. If there are 2 coding *chunks*, - it means 2 OSDs can be out without losing data. - -*N* - the number of data *chunks* plus the number of coding *chunks*, - i.e. *K+M*. - -*rate* - the proportion of the *chunks* that contains useful information, i.e. *K/N*. - For instance, for *K* = 9 and *M* = 3 (i.e. *K+M* = *N* = 12) the rate is - *K* = 9 / *N* = 12 = 0.75, i.e. 75% of the chunks contain useful information. - -The definitions are illustrated as follows (PG stands for placement group): -:: - - OSD 40 OSD 33 - +-------------------------+ +-------------------------+ - | shard 0 - PG 10 | | shard 1 - PG 10 | - |+------ object O -------+| |+------ object O -------+| - ||+---------------------+|| ||+---------------------+|| - stripe||| chunk 0 ||| ||| chunk 1 ||| ... - 0 ||| stripe 0 ||| ||| stripe 0 ||| - ||+---------------------+|| ||+---------------------+|| - ||+---------------------+|| ||+---------------------+|| - stripe||| chunk 0 ||| ||| chunk 1 ||| ... - 1 ||| stripe 1 ||| ||| stripe 1 ||| - ||+---------------------+|| ||+---------------------+|| - ||+---------------------+|| ||+---------------------+|| - stripe||| chunk 0 ||| ||| chunk 1 ||| ... - 2 ||| stripe 2 ||| ||| stripe 2 ||| - ||+---------------------+|| ||+---------------------+|| - |+-----------------------+| |+-----------------------+| - | ... | | ... | - +-------------------------+ +-------------------------+ - -Table of content ----------------- - -.. toctree:: - :maxdepth: 1 - - Developer notes <erasure_coding/developer_notes> - Jerasure plugin <erasure_coding/jerasure> - High level design document <erasure_coding/ecbackend> |