On Fri, 26 Oct 2012, Wido den Hollander wrote: > On 10/25/2012 03:30 PM, Stephen Perkins wrote: > > Hi all, > > > > In looking at the design of a storage brick (just OSDs), I have found a dual > > power hardware solution that allows for 10 hot-swap drives and has a > > motherboard with 2 SATA III 6G ports (for the SSDs) and 8 SATA II 3G (for > > physical drives). No RAID card. This seems a good match to me given my > > needs. This system also supports 10G Ethernet via an add in card, so please > > assume that for the questions. I'm also assuming 2TB or 3TB drives for the > > 8 hot swap. My workload is throughput intensive (writes mainly) and not IOP > > heavy. > > > > I have 2 questions and would love to hear from the group. > > > > Question 1: What is the most appropriate configuration for the journal SSDs? > > > > I'm not entirely sure what happens when you lose a journal drive. If the > > whole brick goes offline (i.e. all OSDs stop communicating with ceph), does > > it make since to configure the SSDs into RAID1? > > > > When you loose the journal these OSDs will commit suicide and in this case > you'd loose 8 OSDs. One small correction here: it depends. If you use ext4 or XFS, then yes: losing the journal means the data disk is lost too. However, if you use btrfs, the data disk has consistent point-in-time checkpoints it can roll back to. It is not useful from the perspective of a specific IO request (i.e., if client X wrote to 3 replicas, then all 3 replicas lost their journals, the write may have been lost, along with the other 0.01% of writes that happened in the last several seconds). On the other hand, for a single osd that loses the journal, you can initialize a new one and it can rejoin the cluster and will have 99.99% of the data in place, making reintegration/recovery quick and cheap sage -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
