[CentOS] drbd strategy

Sat May 31 11:55:20 UTC 2008
Johnny Hughes <johnny at centos.org>

sbeam wrote:
> I have an existing in-production LAMP server running Centos 5.1. It uses 
> physical partitions on top of hardware RAID1, having / /home /var and /boot 
> on separate partitions.
> We have a near-identical system I am thinking of bringing in as a 
> DRBD/Heartbeat companion. One solution may be to use csync2 
> [http://oss.linbit.com/csync2/] on /etc and /usr/local (the only areas that 
> will differ from the stock CentOS). Then setup DRBD for /home and /var.
> From reading the docs it seems we have to use "external meta data" on the 
> existing partitions. Other than that, anyone have any caveats or better ideas 
> for this setup?
> Also - each has 2 NICs. Can Heartbeat do its pinging over the WAN (eth0) with 
> eth1 dedicated to DRBD only? Is that how it is supposed to be, or should we 
> use the serial ports?

One KEY thing to understand about DRBD is that for the normal mode you 
CAN NOT mount the shared partitions on BOTH machines at the same time. 
(DRBD does have an active/active mode, but that is not it's major 
purpose ... DRBD is raid1 for partitions, so just like you can not write 
/ mount BOTH mirrors of a raid1 drive at the same time, you can't do 
that on DRBD either.)

If you really are trying to get a failover machine where you do not need 
to have both partitions mounted and active at the same time, then DRBD 
is probably what you are looking for.

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