> > This is a very good point that I totally overlooked. I concentrated > > more on the IOPS alignment plus write durability, and forgot to check > > the sequential write bandwidth. The 400GB Intel S3700 is a lot more > > faster but double the price (around $950) compared to the 200GB. > Indeed, thus my suggestion of 4 200GBs (at about 1.4GB/s). > Still not a total match, but a lot closer. Also gives you a nice 1:3 > ratio of SSDs to HDDs, meaning that the load and thus endurance is > balanced. > With uneven numbers of HDDs one of your journal SSDs will wear > noticeably earlier than the others. > A dead SSD will also just bring down 3 OSDs in that case (of course the > HDDS are much more likely to fail, but a number to remember). >
Thanks, that 1:3 ration with 200GB SSDs may still fit into our budget. Also, good point on the unbalanced journal partitions. > There's one thing I forgot to mention which makes 2) a bit inferior to > 1) and that is density, as in 3U cases are less dense than 2U or 4U > ones. > For example 12U of 2) will give you 64 drive bays instead of 72 for 1). > > > Maybe I would > > be better off using enterprise SLC SSDs for journals? For example OCZ > > Deneva 2 C 60GB SLC costs around $640, and have 75K write IOPS and > > ~510MB/s write bandwidth by spec. > > > The fact that they don't have power-loss protection will result in loud > cries of woe and doom in this ML. ^o^ > Woa, i didn't know that! It would be funny to loose entire Ceph cluster data in case of power cut due to corruption of the majority of journal filesystems.. > As they don't give that data on their homepage, I would try to find > benchmarks that include what its latency and variances are, the DC 3700s > deliver their IOPS without any stutters. > The eMLC version of the OCZ Deneva 2 didn't perform that well during stress test, the actual results were much below the expected: http://www.storagereview.com/ocz_deneva_2_enterprise_ssd_review Regards, Benjamin _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
