On 08/14/2017 12:52 PM, Ashley Merrick wrote:
Hello,
Hi Ashley!
Currently run 10x4TB , 2xSSD for Journal, planning to move fully to BS,
looking at adding extra servers.
With the removal of the double write on BS and from the testing so far
of BS (having WAL & DB on SSD Seeing very minimal SSD use)
Does it make sense for further servers to go with 12*4TB and get the
benefit of an extra 2 spinning disk per a server over what seems to be
the smaller benefit of having the WAL and DB now on SSD.
Depends on your use case. Small IOs under the min_alloc size (64k by
default for HDDs) will still suffer the double write penalty. You can
tweak it to be smaller, but by decreasing it you increase the amount of
metadata. With bluestore you can put both the WAL (more or less the
equivalent of the journal in FS) and the KeyValueDB store (including
OMAP!) on flash. Bluestore will automatically roll KV data over to the
block disk when your flash DB partition fills up.
For some workloads like small object RGW, having the DB and WAL on flash
yields a pretty significant performance advantage in bluestore. It has
higher and significantly more stable average performance characteristics
vs filestore for continuous small object write workloads.
For other workloads like large sequential reads/writes to RBD volumes,
having flash journal and WAL likely won't help as much. For small
random writes to RBD however, you might still want flash for the WAL/DB.
Mark
Thanks,
Ashley
Sent from my iPhone
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