[DRBD-user] 3 simple questions for a nifty setup

Lars Ellenberg Lars.Ellenberg at linbit.com
Wed Aug 24 19:59:44 CEST 2005

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

/ 2005-08-24 18:34:25 +0100
\ paddy:

thank you for this nice little summary.
some notes:

note that a softlink from /var/lib/mysql to some directory on the drbd
volume would be fine, too.

> I've cobbled together a nasty trick with bind to fail over a dns name, so 
> that a writer can access the db from the secondary node. 

use an alias ip as service address, and fail over the ip.  have this
cluster ip address in dns.  nobody cares which of the nodes currently
has the cluster address.

> There is also the issue of whether a commit propagates correctly.  My assumption
> would be that mysql would return from a commit only after some reasonably 
> conservative effort has been made to write the necessary data to disk and 
> that drbd protocol A will thus guarantee that the commit is written both sides.

protocol _C_ is the transaction safe one.
  A --> asynchronous (unsafe),
  C -> commit safe (synchronous),
  and B somewhere in between...

> > Anybody actually doing this?
> yes :)


> Sorry, I missed the bit earlier about having multiple secondaries in drbd.
> As you know, I had assumed that this is not possible with 0.7, but I don't
> recall exactly why.

in short, because reliable multicast is tricky.

we have paying customers where we do a "tripple legged, two secondary" setup,
but that is currently no so much for availability than for desaster recovery
backup purposes.

: Lars Ellenberg                                  Tel +43-1-8178292-0  :
: LINBIT Information Technologies GmbH            Fax +43-1-8178292-82 :
: Schoenbrunner Str. 244, A-1120 Vienna/Europe   http://www.linbit.com :
please use the "List-Reply" function of your email client.

More information about the drbd-user mailing list