[CentOS] Mirroring Hard Drive

Sat Aug 2 20:03:46 UTC 2008
John R Pierce <pierce at hogranch.com>

Bent Terp wrote:
> On Sat, Aug 2, 2008 at 4:00 PM, Johnny Hughes <johnny at centos.org> wrote:
>> stupid question ... why not just put it in the machine and make it a raid1
>> mirror
> cuz it's not an md volume to begin with?

one method is to make the 2nd disk a 'half' mirror, with all the same 
partitions, then use dump|restore to copy your file systems over to it, 
fix up the grub boot on it, edit teh fstab on this new volume to refer 
to the md sets, then swap it and make it the primary drive, and add the 
original drive as the mirror.

if uptime is your goal, don't forget to mirror the swap too.  too many 
people seem to think thats uneccessary, but if a drive containing 
unmirrored swap dies, the system can only crash and burn (eg, panic).

now, do note, a mirror is ONLY good for protecting against physical 
drive failure, and maintaining uptime, its /NOT/ a substitute for 
backups, as a software glitch, or user error can wipe the mirror out 
just as quick as can be.