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> Ceph might be more usable after Bluestore comes along (at the moment erasure coding performance seems to be pretty bad, even with an SSD cache)

I just saturated a 10Gb link in a k=4,m=2 EC configuration on Ceph (Haswell). Too lazy to set up concurrent clients. What do you mean by pretty bad? This is a Hammer cluster without SSD journals or cache.

Bluestore was recently released with Jewel, but shouldn't affect EC performance drastically, if at all.

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Maybe I'm doing something horribly wrong. My setup was:

- 6x4TB HDD

- 2x120GB SSD

- OSD per disk

- k=4,m=2 erasure coded HDD pool

- 1 copy replicated (not) SSD pool

- SSD pool writeback cache for HDD pool

I was consistently seeing the SSD writeback cache fill up then the disks thrashed at 100% IO utilization, limiting incoming writes to ~40MB/s from memory.

Oops, didn't see this reply until now. It's no longer recommended to use a SSD cache pool, much for the reasons you describe.

You will be a lot better off using bcache or similar, on top of the OSD device.

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