Sage,
Here is some estimate probably how much extra (space wise) we are writing with Bluestore. Considering Rocksdb has not much space amp for level style compaction , these are mostly the metadata Bluestore is writing.
BlueStore:
----------------
root@stormeap-1:~/fio_rbd/fio/examples# ceph df
2016-08-17 11:00:57.936952 7f5c39a2b700 -1 WARNING: the following dangerous and experimental features are enabled: bluestore,rocksdb
2016-08-17 11:00:57.939969 7f5c39a2b700 -1 WARNING: the following dangerous and experimental features are enabled: bluestore,rocksdb
2016-08-17 11:00:57.941269 7f5c39a2b700 -1 WARNING: the following dangerous and experimental features are enabled: bluestore,rocksdb
GLOBAL:
SIZE AVAIL RAW USED %RAW USED
106T 22411G 86867G 79.49
POOLS:
NAME ID USED %USED MAX AVAIL OBJECTS
recovery_test 1 39062G 71.49 6290G 10000003
So, if we trust the statfs implementation of Bluestore , it is writing ~8743 GB more. Total data = image size of 39062 GB * replication 2 = ~78124 GB. So, ~11.19% more.
BTW, this is after 1MB image preconditioning only, filling with 4K blocksize will be adding more metadata.
Filestore:
-----------
GLOBAL:
SIZE AVAIL RAW USED %RAW USED
109T 34443G 78147G 69.41
POOLS:
NAME ID USED %USED MAX AVAIL OBJECTS
recovery_test 2 39062G 69.39 12930G 10000003
So, in the similar setup , filestore is writing only ~23GB extra and i.e ~0.029%
Thanks & Regards
Somnath
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