On Mon, Nov 10, 2014 at 10:58 PM, Christian Balzer <ch...@gol.com> wrote: > > Hello, > > One of my clusters has become busy enough (I'm looking at you, evil Window > VMs that I shall banish elsewhere soon) to experience client noticeable > performance impacts during deep scrub. > Before this I instructed all OSDs to deep scrub in parallel at Saturday > night and that finished before Sunday morning. > So for now I'll fire them off one by one to reduce the load. > > Looking forward, that cluster doesn't need more space so instead of adding > more hosts and OSDs I was thinking of a cache pool instead. > > I suppose that will keep the clients happy while the slow pool gets > scrubbed. > Is there anybody who tested cache pools with Firefly and compared the > performance to Giant? > > For testing I'm currently playing with a single storage node and 8 SSD > backed OSDs. > Now what very much blew my mind is that a pool with a replication of 1 > still does quite the impressive read orgy, clearly reading all the data in > the PGs. > Why? And what is it comparing that data with, the cosmic background > radiation?
Yeah, cache pools currently do full-object promotions whenever an object is accessed. There are some ideas and projects to improve this or reduce its effects, but they're mostly just getting started. At least, I assume that's what you mean by a read orgy; perhaps you are seeing something else entirely? Also, even on cache pools you don't really want to run with 1x replication as they hold the only copy of whatever data is dirty... -Greg _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
