[Users] Re: openvz with OCFS2

Tim Small tim at seoss.co.uk
Wed Jan 12 04:36:08 EST 2011


On 11/01/11 10:23, Aleksandar Ivanisevic wrote:
> Tim Small <tim at seoss.co.uk> writes:
>   
>> We don't currently use drbd in multi-master mode, instead we have a
>> number of drbds per node pair, and all the VEs associated with a given
>> drbd must run on the same node at the same time.
>>     
> Thats exactly what I'm doing too. Why do you need ocfs2 then?
>   

We don't - we just use ext3 on DRBD.

>> Another way to solve the problem would be to use similar methods to
>> OCFS2 etc. (AFAIK) i.e. corosync instead of heartbeat (and use more than
>> two nodes in your corosync totem ring) and set your quorum to prevent
>> split-brain occurring at all.
>>     
> I thought about that, but since drbd doesn't support more than 2
> nodes, I don't really know how that would work.
>   

You don't have to have all machines in the cluster be drbd nodes - in
the simplest case, I believe you could just have a third machine which
just votes.

node A runs drbd, as does node B

node C doesn't, it just takes part in voting etc.

If node A loses connectivity, then it shuts down it services since it
has lost quorum.  B+C together still have quorum, so B continues to
work.  If there were any late changes committed to A, they will be
discarded on reconnect.

... I believe - I haven't had to implement this yet.

Another possibility would be to have three nodes, all doing stuff:

nodes A, B, C

Each node has it's storage pool split into 4 DRBDs (or 4 sets of DRBDs
if you'd prefer - there are certain advantages+disadvantages of doing it
that way).

drbd x1 is hosted by A and B (normally on A)
drbd x2 is hosted by A and B (normally on B)
drbd y1 is hosted by A and C (normally on A)
drbd y2 is hosted by A and C (normally on C)
drbd z1 is hosted by B and C (normally on B)
drbd z2 is hosted by B and C (normally on C)

Quorum is 2.

If node A dies or gets isolated, then B and C take on A's work.

Both B and C end up doing 50% more work than it was before node A died.

HTH.

Cheers,

Tim.

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