[ale] Raid

[Danny Cox]

Greg,

On Sat, 2003-06-21 at 20:43, Greg wrote:
> I have a question on Linux software raid, if I get 3 HD's and set them up
> for RAID 5 - HD # 1 for parity and HD's 2 & 3 for storage and they are all
> 60 GB hard drives, can I add a fourth hard drive later ?  This would give me
> HD #1 for parity and HD's 2, 3, and 4 for storage.

	Well, RAID 4 reserves one drive for parity, which is as you describe,
but that makes the parity drive a bottleneck, which is why RAID 5
exists.  RAID 5 moves the parity drive around.

	Now, yes, you *can* add another driver later, with some caveats.  See
Raidreconf.  It's part of the raidtools package, now.  You MUST backup
your data first.  The general steps would be:

	1) backup your data
	2) install the new drive
	3) construct a new raidtab describing the new setup
	4) shutdown the RAID
	5) run raidreconf
	6) move the new raidtab to /etc/raidtab
	7) start the RAID
	8) watch while it's reconstructing the parity blocks (you can still use
it, though)

	AS OPPOSED TO:

	1) backup your data
	2) install the new drive
	3) modify the raidtab
	4) run mkraid
	5) run mkfs
	6) restore the data

Using raidreconf saves only one copy of the data.  Neither way is
significantly faster than the other.  Notice I didn't specify to what
you backup up your data to ;-).

	HTH!

-- 
kernel, n.: A part of an operating system that preserves the
medieval traditions of sorcery and black art.

Danny

_______________________________________________
Ale mailing list
Ale at ale.org
http://www.ale.org/mailman/listinfo/ale