[ClusterLabs] Question on sharing data with DRDB

[Digimer]

On 2019-03-20 2:31 p.m., Valentin Vidic wrote:
> On Wed, Mar 20, 2019 at 02:01:07PM -0400, Digimer wrote:
>> On 2019-03-20 2:00 p.m., Valentin Vidic wrote:
>>> On Wed, Mar 20, 2019 at 01:47:56PM -0400, Digimer wrote:
>>>> 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).
>>>
>>> The situation I had in mind is this: node1 is Primary and sends a write to
>>> local disk and over the DRBD link. The network fails so the write is
>>> successfull only on the local disk. node1 is than fenced and node2 takes
>>> over but the disk have now diverged.
>>
>> This is handled by using Protocol C in DRBD. That tells DRBD to not
>> consider a write complete until it has hit persistent storage on both nodes.
> 
> Right, but I'm not sure how this would help in the above situation
> unless the DRBD can undo the local write that did not succeed on the
> peer?

So say a write was in flight and the node blew itself up before the
write made it to the peer. That write would not have completed, so the
usual tools to recovery would work (FS journal, database WAL, etc).
Recovering on the backup node would be basically a recovery from a
sudden reboot.

-- 
Digimer
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