[DRBD-user] Drbd mysql

[Lars Ellenberg]

On Wed, Aug 22, 2007 at 04:48:07PM +0200, Pierguido wrote:
> Hi all.
> I'm trying to set up a little cluster with drbd and mysql.
> Reading on the mysql site, i found "MySQL does not support Active/Active 
> configurations using DRBD “out of the box”".
> Does that mean that mysql has some problem with a primary/primary drbd 
> setup?

step back a little.
one single computer.
one mysql instance.
one data directory.

great.

can you add a second mysql instance,
on the same box,
using the same data directory?

no.

so replicating it using drbd and a cluster file system,
and then simultaneously accessing it with a second mysql instance
on a second box
can not magically make it work.

to have more than one application instance access the same data source,
they have to coordinate access,
whether they run on a single host, or on two different hosts.
not only writes (that should be obvious),
but also reads, to avoid cache coherency issues.

if the application does not provide such a coordination layer,
it won't work.

this is not limited to mysql.
your application has to be "cluster aware" to do this.


-- 
: Lars Ellenberg                            Tel +43-1-8178292-0  :
: LINBIT Information Technologies GmbH      Fax +43-1-8178292-82 :
: Vivenotgasse 48, A-1120 Vienna/Europe    http://www.linbit.com :
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