Well, in fact, I think you can't use snapshot with cluster filesystem: as each qemu instance will write in its own snapshot and will not see modifications made by other, and I don't think there is currently a way to share snapshot between qemu instances.
Laurent Le lundi 07 janvier 2008 à 11:42 -0500, Javier Guerra a écrit : > On 1/7/08, Laurent Vivier <[EMAIL PROTECTED]> wrote: > > Le lundi 07 janvier 2008 à 11:03 -0500, Javier Guerra a écrit : > > > hopefully, it would now work with "-cache=off", don't you think? > > > > Well, I don't think the problem is at the host level but at the guest > > level, because both instances of qemu share the host cache and thus > > first instance should see changes made by the second instance (and > > vice-versa). > > that's what a cluster filesystem is designed to cope with (and in fact > expects) > > > There are also some caches at qemu level to emulate DMA, for instance in > > hw/ide.c it is MAX_MULT_SECTORS (16) which is 8 kB buffer, perhaps your > > problem is here but "cache=off" doesn't remove this. > > Did you try to change MAX_MULT_SECTORS to 1 ? > > nope, don't know enough of qemu internals... > > but if those caches can be flushed from the guest, the filesystem > should do that when writing its metadata > > > What do you call a "cluster filesystem" ? > > GFS, OCFS2, etc. that is, filesystems that are designed to run on > more than one host with shared block storage. usually that means > FibreChannel or iSCSI, but on VMs, a common backing could work too (at > least in theory). > > Xen manages it, at least on paravirtualized guests; hadn't tried on > HVM guests. maybe the IDE-like emulation is too poor an interface to > handle it. > -- ----------------- [EMAIL PROTECTED] ------------------ "La perfection est atteinte non quand il ne reste rien à ajouter mais quand il ne reste rien à enlever." Saint Exupéry
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