Dear Cephalopods, In a few weeks we will receive a batch of 200GB Intel DC S3700’s to augment our cluster, and I’d like to hear your practical experience and discuss options how best to deploy these.
We’ll be able to equip each of our 24-disk OSD servers with 4 SSDs, so they will become 20 OSDs + 4 SSDs per server. Until recently I’ve been planning to use the traditional deployment: 5 journal partitions per SSD. But as SSD-day approaches, I growing less comfortable with the idea of 5 OSDs going down every time an SSD fails, so perhaps there are better options out there. Before getting into options, I’m curious about real reliability of these drives: 1) How often are DC S3700's failing in your deployments? 2) If you have SSD journals at a ratio of 1 to 4 or 5, how painful is the backfilling which results from an SSD failure? Have you considered tricks like increasing the down out interval so backfilling doesn’t happen in this case (leaving time for the SSD to be replaced)? Beyond the usually 5 partitions deployment, is anyone running a RAID1 or RAID10 for the journals? If so, are you using the raw block devices or formatting it and storing the journals as files on the SSD array(s)? Recent discussions seem to indicate that XFS is just as fast as the block dev, since these drives are so fast. Next, I wonder how people with puppet/chef/… are handling the creation/re-creation of the SSD devices. Are you just wiping and rebuilding all the dependent OSDs completely when the journal dev fails? I’m not keen on puppetizing the re-creation of journals for OSDs... We also have this crazy idea of failing over to a local journal file in case an SSD fails. In this model, when an SSD fails we’d quickly create a new journal either on another SSD or on the local OSD filesystem, then restart the OSDs before backfilling started. Thoughts? Lastly, I would also consider using 2 of the SSDs in a data pool (with the other 2 SSDs to hold 20 journals — probably in a RAID1 to avoid backfilling 10 OSDs when an SSD fails). If the 10-1 ratio of SSDs would perform adequately, that’d give us quite a few SSDs to build a dedicated high-IOPS pool. I’d also appreciate any other suggestions/experiences which might be relevant. Thanks! Dan -- Dan van der Ster || Data & Storage Services || CERN IT Department -- _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
