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diff --git a/src/ceph/doc/dev/bluestore.rst b/src/ceph/doc/dev/bluestore.rst deleted file mode 100644 index 91d71d0..0000000 --- a/src/ceph/doc/dev/bluestore.rst +++ /dev/null @@ -1,85 +0,0 @@ -=================== -BlueStore Internals -=================== - - -Small write strategies ----------------------- - -* *U*: Uncompressed write of a complete, new blob. - - - write to new blob - - kv commit - -* *P*: Uncompressed partial write to unused region of an existing - blob. - - - write to unused chunk(s) of existing blob - - kv commit - -* *W*: WAL overwrite: commit intent to overwrite, then overwrite - async. Must be chunk_size = MAX(block_size, csum_block_size) - aligned. - - - kv commit - - wal overwrite (chunk-aligned) of existing blob - -* *N*: Uncompressed partial write to a new blob. Initially sparsely - utilized. Future writes will either be *P* or *W*. - - - write into a new (sparse) blob - - kv commit - -* *R+W*: Read partial chunk, then to WAL overwrite. - - - read (out to chunk boundaries) - - kv commit - - wal overwrite (chunk-aligned) of existing blob - -* *C*: Compress data, write to new blob. - - - compress and write to new blob - - kv commit - -Possible future modes ---------------------- - -* *F*: Fragment lextent space by writing small piece of data into a - piecemeal blob (that collects random, noncontiguous bits of data we - need to write). - - - write to a piecemeal blob (min_alloc_size or larger, but we use just one block of it) - - kv commit - -* *X*: WAL read/modify/write on a single block (like legacy - bluestore). No checksum. - - - kv commit - - wal read/modify/write - -Mapping -------- - -This very roughly maps the type of write onto what we do when we -encounter a given blob. In practice it's a bit more complicated since there -might be several blobs to consider (e.g., we might be able to *W* into one or -*P* into another), but it should communicate a rough idea of strategy. - -+--------------------------+--------+--------------+-------------+--------------+---------------+ -| | raw | raw (cached) | csum (4 KB) | csum (16 KB) | comp (128 KB) | -+--------------------------+--------+--------------+-------------+--------------+---------------+ -| 128+ KB (over)write | U | U | U | U | C | -+--------------------------+--------+--------------+-------------+--------------+---------------+ -| 64 KB (over)write | U | U | U | U | U or C | -+--------------------------+--------+--------------+-------------+--------------+---------------+ -| 4 KB overwrite | W | P | W | P | W | P | R+W | P | N (F?) | -+--------------------------+--------+--------------+-------------+--------------+---------------+ -| 100 byte overwrite | R+W | P | W | P | R+W | P | R+W | P | N (F?) | -+--------------------------+--------+--------------+-------------+--------------+---------------+ -| 100 byte append | R+W | P | W | P | R+W | P | R+W | P | N (F?) | -+--------------------------+--------+--------------+-------------+--------------+---------------+ -+--------------------------+--------+--------------+-------------+--------------+---------------+ -| 4 KB clone overwrite | P | N | P | N | P | N | P | N | N (F?) | -+--------------------------+--------+--------------+-------------+--------------+---------------+ -| 100 byte clone overwrite | P | N | P | N | P | N | P | N | N (F?) | -+--------------------------+--------+--------------+-------------+--------------+---------------+ |