Hi, On 01.05.2015 10:30, Piotr Wachowicz wrote: > Is there any way to confirm (beforehand) that using SSDs for journals > will help? yes SSD-Journal helps a lot (if you use the right SSDs) for write speed, and I made the experiences that this also helped (but not too much) for read-performance. > > We're seeing very disappointing Ceph performance. We have 10GigE > interconnect (as a shared public/internal network). Which kind of CPU do you use for the OSD-hosts? > > We're wondering whether it makes sense to buy SSDs and put journals on > them. But we're looking for a way to verify that this will actually > help BEFORE we splash cash on SSDs. I can recommend the Intel DC S3700 SSD for journaling! In the beginning I started with different much cheaper models, but this was the wrong decision. > > The problem is that the way we have things configured now, with > journals on spinning HDDs (shared with OSDs as the backend storage), > apart from slow read/write performance to Ceph I already mention, > we're also seeing fairly low disk utilization on OSDs. > > This low disk utilization suggests that journals are not really used > to their max, which begs for the questions whether buying SSDs for > journals will help. > > This kind of suggests that the bottleneck is NOT the disk. But,m yeah, > we cannot really confirm that. > > Our typical data access use case is a lot of small random read/writes. > We're doing a lot of rsyncing (entire regular linux filesystems) from > one VM to another. > > We're using Ceph for OpenStack storage (kvm). Enabling RBD cache > didn't really help all that much. The read speed can be optimized with an bigger read ahead cache inside the VM, like: echo 4096 > /sys/block/vda/queue/read_ahead_kb Udo _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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