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xen-users
Re: [Xen-users] remus vs. pacemaker/drbd?
Nick Couchman wrote:
It's worth noting that these are slightly different solutions. Remus keeps a
running (but paused), completely synchronized version of your domU(s), and,
when it senses that the original domU is not available, unpauses the standby
domU from it's last synchronized state. This is really any extension of live
migration, as remus is just continually live migrating your memory and disk
data, but never shuts down the original or unpauses the standby version unless
something happens to the original. Pacemaker/DRBD, on the other hand, just
synchronizes the data, and if it detects that one of the domUs has died, starts
it up somewhere else. So, with Remus, the theory/goal is 0 downtime of your
domU, whereas Pacemaker simply minimizes downtime to a certain point - the time
it takes to detect failure and boot the new domU.
Understood.
In my case, I'm running Pacemaker/DRBD and can live with short outages.
But... it's pretty tricky to keep all the pieces configured and running
properly, and I'm not looking forward to the gotchas when it's time to
migrate from Debian Lenny to Debian Squeeze - what with all different
versions, dependencies, and such as one updates first one machine, then
another, while trying to stay live.
Remus looks a lot simpler, at the cost of the resources associated with
running backup VMs. But then again, Pacemaker/DRBD requires that you
have the resources to migrate to - so you need a hot spare machine
anyway. Whether the backup VM is running or not, you need the same
resources - and I assume the network load is similar whether its
generated by Remus or by DRBD.
Which comes back to the question of whether Remus is mature enough to
rely on or not.
Thanks,
Miles
--
In theory, there is no difference between theory and practice.
In<fnord> practice, there is. .... Yogi Berra
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