Hello, see the current "Blocked requests/ops?" thread in this ML, especially the later parts. And a number of similar threads.
In short, the CPU requirement for SSD based pools are significantly higher than for HDD or HDD/SSD journal pools. So having dedicated SSD nodes with less OSDs, faster CPUs and potentially faster network makes a lot of sense. It also helps a bit to keep you and your CRUSH rules sane. In your example you'd have 12 HDD based OSDs with journals, at 1.5-2GHz CPU per OSD (things will get CPU bound with small write IOPS). A SSD (I'm assuming something like DC S3700) based OSD will eat all the CPU you can throw at it, 6-8GHZ would be a pretty conservative number. Search the archives for the latest tests/benchmarks by others, don't take my (slightly dated) word for it. Lastly you may find like other that cache-tiers currently aren't all great performance wise. Christian. On Sat, 30 May 2015 10:36:39 +0200 Martin Palma wrote: > Hello, > > We are planing to deploy our first Ceph cluster with 14 storage nodes > and 3 monitor nodes. The storage node have 12 SATA disks and 4 SSDs. 2 > of the SSDs we plan to use as > journal disks and 2 for cache tiering. > > Now the question raised in our team if it would be better to put all SSDs > lets say in 2 storage nodes and consider them as fast nodes or to > distribute the SSDs for the cache tiering over all 14 nodes (2 per node). > > In mine opinion, if I understood the concept of Ceph right (I'm still in > the learning process ;-) distributing the SSDs across all storage nodes > would be better since this also would distribute the network traffic > (client access) across all 14 nodes and not only limit it to 2 nodes. > Right? > > Any suggestion on that? > > Best, > Martin -- Christian Balzer Network/Systems Engineer ch...@gol.com Global OnLine Japan/Fusion Communications http://www.gol.com/ _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
