[DRBD-user] DRBD and KVM for a HA-Cluster ?

J. Ryan Earl oss at jryanearl.us
Mon Jan 10 19:24:02 CET 2011

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

On Sun, Jan 9, 2011 at 11:00 AM, Lentes, Bernd <
bernd.lentes at helmholtz-muenchen.de> wrote:

> Hi,
> Currently everything is clear.
> Thanks for your help

Yea I was out of pocket for a few days, but basically, you end up with 3
DRBD devices, 1 per VM/service right?  When I said "dual-primary" I was
speaking of DRBD only.  DRBD in "dual-primary" aka "active-active" is
analogous to a "shared storage"--such as a DAS or SAN connected to servers
via HBAs with the same LUN mapped to both servers--modulo split-brain
considerations as explained above.

The reason you make it active-active on both nodes is because with
Live-Migration the VM does exist simultaneously on both nodes for a brief
period of time as the memory pages/state are migrated over and both access
the block device simultaneously yet in a synchronized manner through the
underlying HyperVisor.  Indeed, there is a mechanism in place
for synchronization as your surmised there must be.

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