[ClusterLabs] Question on sharing data with DRDB

Digimer lists at alteeve.ca
Wed Mar 20 13:47:56 EDT 2019

On 2019-03-20 1:46 p.m., Valentin Vidic wrote:
> On Wed, Mar 20, 2019 at 01:34:52PM -0400, Digimer wrote:
>> Depending on your fail-over tolerances, I might add NFS to the mix and
>> have the NFS server run on one node or the other, exporting your ext4 FS
>> that sits on DRBD in single-primary mode.
>> The failover (if the NFS host died) would look like this;
>> 1. Lost node is fenced.
>> 2. DRBD is promoted from Secondary to Primary
>> 3. ext4 FS is mounted.
>> 4. Virtual IP (used for NFS) is brought up.
>> 5. NFS starts
>> Startup and graceful migration would be the same, minus the fence.
> Would it be possible for DRBD to go into SplitBrain if the lost node
> manages to write something to local DRBD disk before it gets fenced?

Not when DRBD is configured correctly. You sent 'fencing
resource-and-stonith;' and set the appropriate fence handler. This tells
DRBD to not proceed with a write while a node is in an unknown state
(which happens when the node stops responding and is cleared on
successful fence).

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