Hi, we had a setup like this and ran into trouble, so I would strongly discourage you from setting it up like this. Under normal circumstances there's no problem, but when the cluster is under heavy load, for example when it has a lot of pgs backfilling, for whatever reason (increasing num of pgs, adding OSDs,..), there's obviously a lot of entries written to the journals. What we saw then was extremly laggy behavior of the cluster and when looking at the iostats of the SSD, they were at 100% most of the time. I don't exactly know what causes this and why the SSDs can't cope with the amount of IOs, but seperating OS and journals did the trick. We now have quick 15k HDDs in Raid1 for OS and Monitor journal and per 5 OSD journals one SSD with one partition per journal (used as raw partition). Hope that helps, best regards, Kurt Martin Catudal schrieb: > Hi, > Here my scenario : > I will have a small cluster (4 nodes) with 4 (4 TB) OSD's per node. > > I will have OS installed on two SSD in raid 1 configuration. > > Is one of you have successfully and efficiently a Ceph cluster that is > built with Journal on a separate partition on the OS SSD's? > > I know that it may occur a lot of IO on the Journal SSD and I'm scared > of have my OS suffer from too much IO. > > Any background experience? > > Martin >
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