[ClusterLabs] Question on sharing data with DRDB

Digimer lists at alteeve.ca
Wed Mar 20 13:44:06 EDT 2019

On 2019-03-20 1:41 p.m., Valentin Vidic wrote:
> On Wed, Mar 20, 2019 at 12:37:21PM -0400, Digimer wrote:
>>   Cluster filesystems are amazing if you need them, and to be avoided if
>> at all possible. The overhead from the cluster locking hurts performance
>> quite a lot, and adds a non-trivial layer of complexity.
>>   I say this as someone who has used dual-primary DRBD with GFS2 for
>> many years.
> If the GFS2 holds qcow2 images, does node1 need to synchronize writes
> to vm1.qcow2 with node2 writing to vm2.qcow2?

GFS2 notified the peers of disk changes, and DRBD handles actually
copying to changes to the peer.

Think of DRBD, in this context, as being mdadm RAID, like how writing to
/dev/md0 is handled behind the scenes to write to both /dev/sda3 +
/dev/sdb3. DRBD is like the same, any writes to /dev/drbd0 is written to
both node1:/dev/sda3 + node2:/dev/sda3.

So DRBD handles replication, and GFS2 handles coordination.

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