On 01/13/15 22:03, Roland Giesler wrote: > I have a 4 node ceph cluster, but the disks are not equally > distributed across all machines (they are substantially different from > each other) > > One machine has 12 x 1TB SAS drives (h1), another has 8 x 300GB SAS > (s3) and two machines have only two 1 TB drives each (s2 & s1). > > Now machine s3 has by far the most CPU's and RAM, so I'm running my > VM's mostly from there, but I want to make sure that the writes that > happen to the ceph cluster get written to the "local" osd's on s3 > first and then the additional writes/copies get done to the network. > > Is this possible with ceph. The VM's are KVM in Proxmox in case it's > relevant.
I don't think it is possible because I believe it would break its durability guarantees: IIRC each write is only considered done when all replicas have been written to (with default settings 3 replicas on 3 different servers) so you have to wait for 3 servers to acknowledge the write for it to complete in the VM. You could maybe achieve what you want by using tiering with a cache pool configured to use only disks on the s3 server in write-back mode but given the user experience reports on the list it may actually perform worse than your current setup. Best regards, Lionel Bouton
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