On Sat, Jan 29, 2011 at 09:54:55PM +0000, John Robinson wrote: > On 29/01/2011 21:08, Alexander Schreiber wrote: > >On Sat, Jan 29, 2011 at 12:23:14PM -0200, Denis wrote: > >>2011/1/29 Alexander Schreiber<als@xxxxxxxxxxxxxxx> > >> > >>> > >>>plain disk performance for writes, while reads should be reasonably > >>>close to the plain disk performance - drbd optimizes reads by just reading > >>>from the local disk if it can. > >>> > >>> > >> However, I have not used it with active-active fashion. Have you? if yes, > >>what is your overall experience? > > > >We are using drbd to provide mirrored disks for virtual machines running > >under Xen. 99% of the time, the drbd devices run in primary/secondary > >mode (aka active/passive), but they are switched to primary/primary > >(aka active/active) for live migrations of domains, as that needs the > >disks to be available on both nodes. From our experience, if the drbd > >device is healthy, this is very reliable. No experience with running > >drbd in primary/primary config for any extended period of time, though > >(the live migrations are usually over after a few seconds to a minute at > >most, then the drbd devices go back to primary/secondary). > > Now that is interesting, to me at least. More as a thought > experiment for now, I was wondering how one would go about setting > up a small cluster of commodity servers (maybe 8 machines) running > Xen (or perhaps now KVM) VMs, such that if one (or potentially two) > of the machines died, the VMs could be picked up by the other > machines in the cluster, and only using locally-attached SATA/SAS > discs in each machine. > > I guess I'm talking about RAIN or RAIS rather than RAID so maybe I'd > better start reading the Wikipedia pages on those and not talk about > it on this list... For the "survive single node total machine failure" case your problem has already been solved: http://code.google.com/p/ganeti/ We run a large number of clusters with that and the VMs routinely survive disk failures and recover (come back from what looks like a power failure to the VM) from node failure. Kind regards, Alex. -- "Opportunity is missed by most people because it is dressed in overalls and looks like work." -- Thomas A. Edison -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
