Hi Adam,

I suggest to set noout before removing the drive, so that cluster doesn't start to rebalance. Then put in the new disk and in it; then unset noout.

That way you just get the network traffic to complete the data in that new disk (copy recover), and no rebalancing.

On 28/10/14 16:05, Adam Thompson wrote:
On 14-10-28 10:03 AM, Adam Thompson wrote:
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?


A related question: to proactively replace a disk, I'm doing Stop->Out->Remove / swap disk / Create OSD. Is that a viable procedure? Other than the rebuild I/O starving regular reads, it seems to be working...



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