Re: [gentoo-amd64] Upgrading to Raid

[Kyle Liddell <kyle@foobox.homelinux.net>]

On Wed, 2005-08-31 at 21:46 -0600, scotthathcock@comcast.net wrote:
> Is there a good Howto on migrating from a non Raid disk to Raid? I
> recall seeing one but can't find it now.

If you're really lazy (like me), you can convert your current running
system over to RAID without messing with reinstalling from backups
(although you probably should make the backups, hopefully you won't have
to use them).  Assuming you're doing RAID1, get your partitions and such
set up on your new drive.  Then set up the raid array (the howto on
tldp.org is helpful, although be sure to use the newer mdadm setup even
though the docs are a little thinner in the howto) on your new drive,
marking the other drive in the array as bad/down.  Copy say, /dev/hdxy
to /dev/mdx, and then edit the proper config files so that when you
reboot you'll be using the raid array.  Once you're in it, change the
other drive in the array from bad to the old drive, and it'll rebuild
the array on the fly.  It's pretty neat.

(If you do that method though, read the docs very carefully to make sure
you're doing it right.  It's been a while since I've done it so I may
have gotten something backwards or some such.)

I wouldn't worry about any performance hits:  A few months ago I
converted an old P2 450mhz system to RAID 1+0 and noticed no performance
hits, and even went to raid1 + lvm and again no problems.  I've since
added an additional CPU to that box, but hard drives are just so much
slower than your CPU that it'd take a lot of work to create a slowdown.

Also, if there's any chance you'll want to maybe resize your partitions,
or especially, add more drives to the system, I would very strongly
suggest looking into LVM (Linux Volume Manager).  It plays well with
raid (instead of raid1+0 I'm doing the equivalent with raid1+lvm, but no
worries about adding more disks) and lets you alter "partitions" on the
fly.  If you want to add more storage, just buy a pair of drives, raid1
them, then just append it to the end of your volume, and run your
favorite on the fly partition resizer and enjoy.

By the way, a $15 promise ATA100 two channel IDE PCI card + a pair of
$80 120gb seagate HDDs is quite a nice deal.  I've got two of the
Promise IDE cards in my server, and they seem to be pretty good PATA
cards if you're into that sort of thing.

Kyle


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