Wow I feel like we got off easy. We're on our second generation of hardware running Jewel:
35 8TB spinners w/collocated journals
Dual 10G nics w/jumbo frames
14.04 on 4.2 kernel
5 RGWs - these are the only clients
This was designed as "warm" object storage with performance secondary to price, hence the lack of flash for journals. Still we've gotten perfectly adequate performance and had nearly 0 problems with it. Jumbo frames, turning off swap and upping
some ulimits are pretty much the only tuning we've had to do. We've gone through recovery from removing 2 nodes with no problems.
when you say "XFS crashes" is it actual crashes, or is it "soft" allocation failures ?
We were "experimenting" with dense nodes, as in 31 x 8TB spinning rust, NVMe journal, 256GB RAM, 40 GigE, and ended up on the wrong end of how linux-xfs reclaims memory.
Our symptoms were packet drops (I forget which direction) and latencies jumping up into the second range when packets were't dropped, which caused osd's to be marked as non-responsive by the cluster, and sometimes this spiraled out of hand. Essentially,
the XFS reclaim were something along the lines of, for each xfs filesystem, try to reclaim without "big fat lock", if that fails, grab "big fat lock" and reclaim. The drives were hideously slow, sadness ensued. In the end, we ended up systemtap'ing the xfs
driver into not grabbing the big fat lock, hoping that it could do reclaim on one of the other XFS filesystems without "big fat lock". It's so far worked really well for us, and our current plan is to leave the ugly hack in place until we feel bluestore is
the way to go.
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