[asterisk-users] High Availability - Shared Database - Ideas?

[Jonathan Thurman]

On Wed, Apr 21, 2010 at 1:09 PM, Robert Grignon <rgrignon at fleetone.com> wrote:
>
> I am investigating High Availability solutions for my front end servers.

Always good to hear.

> I got into a discussion regarding "replicated local databases" versus "
> a single fiber connected shared database" on an EMC.

I will guess that you mean MySQL Master/Slave replication.

> Is anyone running a shared database on a SAN? Care to comment on your
> findings...

I am running MySQL on shared SAN LUN, but not for Asterisk.  Since
SANs are expensive, I have been using DRBD/GFS2/MySQL for most of my
low budget HA Asterisk installations.  Some things to think about:

1. If you are using MySQL, then only one server can have the database
open at a time.  You will have some lag/downtime when the active
server fails and the secondary has to take over.  You are going to
have this anyway even with a Master/Master replication as the IP has
to shift.  Same with Master/Slave plus you add time for a script to
promote the Slave.

2. Don't even think about using MyISAM... InnoDB *only*.  MyISAM
doesn't check improperly closed tables until they are accessed which
can cause some major lag.  Not to mention no transaction support.  You
won't have another copy if things get corrupted (besides all of your
backups of course)

3. While nice SANs are redundant, you are still adding another
dependency to the system (a few if you are using FC switches).  Make
sure everything has multiple paths, and don't forget to configure
fencing for the nodes.

4. If you have PRI/Analog lines to the server, then it becomes more of
a headache.  Use dependable redundant SIP gateways, or have some
action plan in place.

5. Test, test, test then test some more.  Break it in the lab and know
how to fix it.  Setup is easy, repair can be a pain. (You also want to
know it will actually work =)

That's my quick $0.02, and there is a lot more to think about too.
Overall, if designed right I think it is a good option.  Just depends
on your level of comfort with the technologies, and the risk/benefit
that goes along with it.

-Jonathan