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* Bluestore is 2x faster than Filestore in HDD-only (or bad-SSD-only) configurations, because it can do 1 commit per write, at least if you remove the handbrake from here: https://github.com/ceph/ceph/pull/26909 or if you wait for the backport. In fact it’s OK to say that Bluestore’s deferred-write algorithm is really optimal for HDD-only transactional write.
* In HDD+SDD configurations, Bluestore performance is very consistent, but it’s worse than the peak performance of Filestore for the same hardware. This is because Bluestore’s deferred write queue doesn’t act as a «temporary buffer» that can smooth burst random write loads. In other words, Bluestore OSD refuses to do random writes faster than the HDD can do on average.
*: So with Filestore you can easily get temporary 1000—2000 iops with (iodepth=1). But after the journal becomes full it will drop very low, to 30-50 iops. With Bluestore you only get 100-300 iops for a single write thread — or even moreHDD regardless of the SSD journal, but these are absolutely stable over time.*: This is caused by the deferred write queue being very short* In SSD
== RAID WRITE HOLE ==
