Hello Cephers, I am a bit lost on the best ways of using ssd and hdds for ceph cluster which uses rbd + kvm for guest vms.
At the moment I've got 2 osd servers which currently have 8 hdd osds (max 16 bays) each and 4 ssd disks. Currently, I am using 2 ssds for osd journals and I've got 2x512GB ssd spare, which are waiting to be utilised. I am running Ubuntu 12.04 with 3.13 kernel from Ubuntu 14.04 and the latest firefly release. I've tried to use ceph cache pool tier and the results were not good. My small cluster slowed down by quite a bit and i've disabled the cache tier altogether. My question is how would one utilise the ssds in the best manner to achieve a good performance boost compared to a pure hdd setup? Should I enable block level caching (likes of bcache or similar) using all my ssds and do not bother using ssd journals? Should I keep the journals on two ssds and utilse the remaining two ssds for bcache? Or is there a better alternative? Cheers Andrei
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