drbd-user March 2010 archive
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drbd-user: Re: [DRBD-user] dual primary mode with which FS

Re: [DRBD-user] dual primary mode with which FS

From: Florian Haas <florian.haas_at_nospam>
Date: Tue Mar 23 2010 - 18:50:07 GMT
To: drbd-user@lists.linbit.com

On 03/23/2010 07:35 PM, Michael Schwartzkopff wrote:
> Am Dienstag, 23. März 2010 17:08:56 schrieb Digimer:
>> On 10-03-23 10:02 AM, Florian Haas wrote:
>>> On 2010-03-23 14:52, Michael Schwartzkopff wrote:
>>>> Am Freitag, 19. März 2010 14:12:30 schrieb Andreas.Ruetten@hansenet.com:
>>>>> Hi list,
>>>>>
>>>>> first of all please answer also to my email-address because I'm not
>>>>> subscribed to the ML.
>>>>>
>>>>> Here are my questions:
>>>>>
>>>>> I have to set up drbd 8.0.14 (Debian stable) in dual-primary mode.
>>>>> One node has to read and write while the other node only need read
>>>>> access.
>>>>>
>>>>> Do I need GFS or OCFS?
>>>> Not really if you can be sure that the second node ONLY reads.
>>> Are you nuts? I thought you wrote books about this!
>>>
>>>>> Or would a simple etx3 sufficient enough?
>>>> Yes. Mount option "read-only" in the second node.
>>> I repeat my above statement.
>>>
>>> I'm totally baffled right now.
>>>
>>> Andreas: you want to put a filesystem on dual-Primary DRBD, it has to be
>>> a cluster filesystem. No ifs, buts, or maybes.
>>>
>>> Question is, do you really need dual-Primary DRBD? You most probably
>>> don't.
>>>
>>> Florian
>> From a purely technical view point, Michael isn't wrong. If the second
>> node never changes a single block on the DRBD partition, it can't
>> technically hurt it. Of course, you'd need to make sure that the node's
>> DRBD doesn't try to recover from failures without first fencing the
>> other node.
>>
>> It's not wise, but it's not impossible, either.
>
> didn't have my best day today. Although it should be possbile I did not say it
> is wise to do.

To wrap this up: don't do this. Ever. The reasons have been mentioned in
this thread. Data divergence, and violation of cache coherency.

Florian

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