[DRBD-user] Drbd mysql

Michael Tewner tewner at gmail.com
Thu Aug 23 07:44:19 CEST 2007


What we did:
we have DRBD in an primary/primary configuration for our postfix. At
the same time, we use heartbeat to keep *one* MySQL instance running
on either of our two nodes, grouped with an IP. MySQL is configured to
access that IP.

If one computer or Mysql Dies, heatbeat migrates it to the other node,
with it's IP, and the not-dead node continues working happily  with
mysql locally.

On 8/23/07, alex at crackpot.org <alex at crackpot.org> wrote:
> Quoting Lars Ellenberg <lars.ellenberg at linbit.com>:
>
> > 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.
>
> You can do this if you configure MySQL to use external locking.
>
> You are limited to only MyISAM tables (no foreign keys, no
> transactions, only table-level locking).  I've used this to play
> around with running 2 MySQL daemons on the same box with the same data
> files.  I have no idea how well it performs 'for real'.  I'd be a
> little scared to find out...  But if someone feels like experimenting
> it can be done.
>
> http://dev.mysql.com/doc/refman/5.0/en/external-locking.html
>
> alex
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