2013-08-09 21:23:17 +00:00
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==============================
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Erasure Coded Placement Groups
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==============================
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2013-07-31 21:38:59 +00:00
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2013-08-09 21:23:17 +00:00
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The documentation of the erasure coding implementation in Ceph was
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created in July 2013. It is included in Ceph even before erasure
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coding is available because it drives a number of architectural
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changes. It is meant to be updated to reflect the `progress of these
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architectural changes <http://tracker.ceph.com/issues/4929>`_, up to
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the point where it becomes a reference of the erasure coding
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implementation itself.
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2013-07-31 21:38:59 +00:00
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2013-08-20 14:17:10 +00:00
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Glossary
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--------
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*chunk*
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when the encoding function is called, it returns chunks of the
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same size.
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*stripe*
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when an object is too large to be encoded with a single call,
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each set of chunks created by a call to the encoding function is
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called a stripe.
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*shard|strip*
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the file that holds all chunks of a same rank for a given object.
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Example:
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::
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2013-08-21 16:09:03 +00:00
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OSD 40 OSD 33
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2013-08-20 14:17:10 +00:00
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+-------------------------+ +-------------------------+
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| shard 0 - PG 10 | | shard 1 - PG 10 |
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|+------ object O -------+| |+------ object O -------+|
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||+---------------------+|| ||+---------------------+||
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stripe||| chunk 0 ||| ||| chunk 1 ||| ...
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0 ||| [0,+N) ||| ||| [0,+N) |||
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||+---------------------+|| ||+---------------------+||
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||+---------------------+|| ||+---------------------+||
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stripe||| chunk 0 ||| ||| chunk 1 ||| ...
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1 ||| [N,+N) ||| ||| [N,+N) |||
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||+---------------------+|| ||+---------------------+||
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||+---------------------+|| ||+---------------------+||
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stripe||| chunk 0 [N*2,+len) ||| ||| chunk 1 [N*2,+len) ||| ...
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2 ||+---------------------+|| ||+---------------------+||
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|+-----------------------+| |+-----------------------+|
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| ... | | ... |
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+-------------------------+ +-------------------------+
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Table of content
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----------------
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2013-08-09 21:23:17 +00:00
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.. toctree::
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:maxdepth: 1
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2013-07-31 21:38:59 +00:00
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2013-08-09 21:23:17 +00:00
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High level design document <erasure_coding/pgbackend>
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Developer notes <erasure_coding/developer_notes>
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2013-08-21 16:09:03 +00:00
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Draft PGBackend.h header <erasure_coding/PGBackend-h>
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