>>If you need caching on the hypervisor side it would probably better to >>use something like bcache/dmcache etc. Not possible in my case, as I use qemu rbd block driver, not the rbd kernel module.
My concern was mainly using librbd cache http://ceph.com/docs/master/rbd/rbd-config-ref/#rbd-cache-config-settings which is enabled with cache=writeback According the doc: " it can coalesce contiguous requests for better throughput." So they are optimisations specific to rbd when it's enabled. (If someone have documentation about how exactly librbd cache is working, I'm interested) ----- Mail original ----- De: "Alex Crow" <ac...@integrafin.co.uk> À: ceph-users@lists.ceph.com Envoyé: Samedi 12 Avril 2014 17:26:40 Objet: Re: [ceph-users] qemu + rbd block driver with cache=writeback, is live migration safe ? Hi. I've read in many places that you should never use writeback on any kind of shared storage. Caching is better dealt with on the storage side anyway as you have hopefully provided resilience there. In fact if your SAN/NAS is good enough it's supposed to be best to use "none" as the caching algo. If you need caching on the hypervisor side it would probably better to use something like bcache/dmcache etc. Cheers Alex On 12/04/14 16:01, Alexandre DERUMIER wrote: > Hello, > > I known that qemu live migration with disk with cache=writeback are not safe > with storage like nfs,iscsi... > > Is it also true with rbd ? > > > If yes, it is possible to disable manually writeback online with qmp ? > > Best Regards, > > Alexandre > _______________________________________________ > ceph-users mailing list > ceph-users@lists.ceph.com > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
