On Mon, Jan 31, 2011 at 06:42:44AM -0200, Denis wrote:
> 2011/1/29 Alexander Schreiber <als@xxxxxxxxxxxxxxx>:
> > 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).
>
> What filesystem are you using to enable the primary-primary mode? Have
> you evaluated it against any other available option?
The filesystem is whatever the VM is using, usually ext3. But the
filesystem doesn't matter in our use case at all, because:
- the backing store for drbd are logical volumes
- the drbd block devices are directly exported as block devices
to the VMs
The filesystem is only active inside the VM - and the VM is not aware of
the drbd primary/secondary -> primary/primary -> primary/secondary dance
that happens "outside" to enable live migration.
Kind regards,
Alex.
--
"Opportunity is missed by most people because it is dressed in overalls and
looks like work." -- Thomas A. Edison
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