[DRBD-user] Two primaries setup over a Wan Network which broke up frequently...

Lars Ellenberg lars.ellenberg at linbit.com
Thu Feb 12 21:43:49 CET 2009

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

On Thu, Feb 12, 2009 at 05:02:32PM +0100, Julien Reveillet wrote:
> Hello,
> I have a very special configuration to set up.
> I need to have 2 servers running CentOs 5 with a mysql server 4.0.21 (
> that a must do...).
> The data base directory needs to be replicated between both servers with
> one mysql server running with read-write access and the other with
> read-only access.
> The production server (mysqld with rw access) which is highly loaded
> needs to not be impacted by drbd accesses ( it can be a little bit ) and
> the web server (mysqld with ro access) can be asynchronous for some
> minutes with no problems.
> For now, i choosed to use drbd 8.2.6 with ocfs2.
> It is set up and running correctly on the same lan with a descent sync
> rate but i will have to try it soon over a wan network.
> On what i've tested and read, i can't use protocol A for this scenario
> as the option "allow-two-primaries" needs only protocol C.
> The whole database directory is about 70GB which is quite huge to full
> sync over a 2M wan network. For sure, i will do the first sync over a
> lan but i'm afraid of cases where drbd will go to standalone and will
> need a full resync.
> So my questions are :
> - Falling to standalone mode will automaticly needs a full resync?

No. Why?

> - Can this kind of scenario be possible to work on or not ?
> (if not, do you think of another solution?)

If you _want_ asynchronous replication,
why would you go for a synchronous replication solution?
why not go for mysql replication, if that is actually what you want?

cluster file lock manager latency and all sorts of issues
with a WAN link will be a real pita.

> - Will protocol C cause many heavy lags on my production server ?
> (i guess yes but...)

the replication link is 2 megabit/second,
which is roughly 200 kByte per second.
and the latency is what?  200 msec?
well, DRBD cannot magically improve those numbers.
I don't think that would be feasibly for a cluster file system.
and not at all for a data base on top of a cluster file system.

: Lars Ellenberg
: LINBIT | Your Way to High Availability
: DRBD/HA support and consulting http://www.linbit.com

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