[PVE-User] excessive I/O latency during CEPH rebuild

[Adam Thompson]

I'm seeing ridiculous I/O latency after out'ing and re-in'ing a disk in 
the CEPH array; the OSD monitor tab shows two OSDs (i.e. disks) having 
latency above 10msec - they're both in the 200ms range - but reading a 
single uncached sector from a virtual disk takes >10sec.

It's bad enough that all my virtualized DNS servers are timing out and 
this, of course, directly impacts service.

During normal (non-rebuild, non-rebalance) operations, CEPH is not 
terribly fast to write, but delivers acceptable read speeds.

Where do I start looking for problems?  Are there any knobs I should be 
tweaking for CEPH?

-- 
-Adam Thompson
  athompso at athompso.net