[ClusterLabs] Antw: Re: Question on sharing data with DRDB

[Ulrich Windl]

>>> Digimer <lists at alteeve.ca> schrieb am 20.03.2019 um 18:47 in Nachricht
<38f790d0-4bb6-53b8-7eb4-b285ed14779d at alteeve.ca>:
> 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

Are your really saying that dual-primary no longer needs operator intervention
after a node crash?
That's also split-brain to me if DRBD does not know how to recover after a
link interruption.

> 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).
> 
> -- 
> Digimer
> Papers and Projects: https://alteeve.com/w/ 
> "I am, somehow, less interested in the weight and convolutions of
> Einstein’s brain than in the near certainty that people of equal talent
> have lived and died in cotton fields and sweatshops." - Stephen Jay Gould
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