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I have a couple of questions about caching: I have 5 VM-Hosts serving 20 VMs. I have 1 Ceph pool where the VM-Disks of those 20 VMs reside as RBD Images. 1) Can i use multiple caching-tiers on the "same" data pool? I would like to use a local SSD OSD on each VM-Host that can serve as "application accelerator" local-cache for the VM-Disks. I can imagine data corruption if other VM-Hosts write to the same Ceph data pool but not using the same caching-tier. I imagine no data corruption if i know no other VM-Hosts will access that Ceph object (VM-Disk / RBD image). I would need to flush the cache of that VM-Host when i shutdown the VM on it, before i can start the VM on a different VM-Host. Or is Ceph perhaps smart enough that it would notify the above Caching-Tier to evict a cached object when there is a change on that object not changed by that caching-tier? 2) RBD Cache is useless for hosting Oracle databases? If Oracle is doing a O_SYNC and RBD Cache would flush on O_SYNC, then there would be nothing cached. Correct? 3) Would a caching tier be smart enough to flush dirty/modified objects on "idle" i/o? (when client i/o is not busy ceph will use that time to sync to backend) I know it will flush on at a certain capacity (50%) or on a certain age (600sec), but can it also flush on a certain busy/idle percentage or auto-magically/intelligently? Thanks, Samuel Terburg Panther-IT BV www.panther-it.nl |
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