[Pacemaker] DRBD and fencing

[Martin Aspeli]

Matthew Palmer wrote:
> On Wed, Mar 10, 2010 at 02:32:05PM +0800, Martin Aspeli wrote:
>> Florian Haas wrote:
>>> On 03/09/2010 06:07 AM, Martin Aspeli wrote:
>>>> Hi folks,
>>>>
>>>> Let's say have a two-node cluster with DRBD and OCFS2, with a database
>>>> server that's supposed to be active on one node at a time, using the
>>>> OCFS2 partition for its data store.
>>> *cringe* Which database is this?
>> Postgres.
>>
>> Why are you cringing? From my reading, I had gathered this was a pretty
>> common setup to support failover of Postgres without the luxury of a
>> SAN. Are you saying it's a bad idea?
>
> PgSQL on top of DRBD is OK.  PgSQL on top of OCFS2 is a disaster waiting to
> gnaw your leg off.

Hah. I'm glad someone told me. ;-)

Why is this?

>> Mmm, you're not:
>> http://fghaas.wordpress.com/2007/06/26/when-not-to-use-drbd :-)
>>
>> Or is it OCFS2 you're objecting to? We're using this because there are a
>> few shared files ("blobs" in our CMS) that get written by processes on
>> both nodes. This is very infrequent, though.
>
> Split them -- put PostgreSQL on a regular filesystem and mount it before
> starting the database, and run a separate dual-primary for your blobs.

Yeah, that's perfectly reasonable.

>> Also note that this database will see relatively few write transactions
>> compared to read transactions, if that makes a difference.
>
> Cluster filesystems suck at high IO request rates, regardless of whether
> they're reads or writes.

Gotcha - so it's mainly a performance issue?

Martin

-- 
Author of `Professional Plone Development`, a book for developers who
want to work with Plone. See http://martinaspeli.net/plone-book