[DRBD-user] DRBD Dual Primary and KVM

Digimer lists at alteeve.ca
Mon Jun 24 18:37:02 CEST 2013

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

First off, do you have fencing/stonith configured? What cluster stack,
if any, are you using at this time?

If the VMs use the raw DRBD resource, then dual-primary alone would be
fine so long as you make sure both nodes never run the VM at the same
time (fencing goes a long way to ensure. If you have files backing the
VMs on a file system, then yes, you would need a clustered file system
like GFS2.

You need dual-primary for live migration, so it's worth getting things
going. However, dual-primary is not a task to be taken lightly. You will
need to test you cluster stack and fencing carefully, avoid fence loops,

There is nothing inherently hard about dual-primary, but it is often
recommended against simply because people don't take the time to do it
right. And when done wrong, it's easy to blow your foot off. :)

On 06/24/2013 12:13 PM, Aaron Clausen wrote:
> I'm currently configuring two KVM host servers and things are going
> along pretty well. I'm story KVM images directly to the drbd devices
> in raw format, and it's working very well with tolerable overhead.
> One thing I am wondering, however, is whether I can safely switch from
> primary/secondary mode to dual primary. I know in most cases you're
> supposed to have a shared cluster file system, but primarily my
> interest here is in quickly migrating from server to the other.
> Removing "drbdadm primary"/"drbdadm secondary" would make things a bit
> easier. As it stands, only one server is going to be accessing the
> drbd device at a time (firing up two guests with the same MACs,
> network configs and the like would be pretty ugly all on its own).
> Or is it simply safer to continue running in primary/secondary mode?
> --
> Aaron Clausen
> mightymartianca at gmail.com
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