Subject: Re: root on raid: re-arranging disks?
From: Mike Tibor (tibor@lib.uaa.alaska.edu)
Date: Thu Dec 06 2001 - 14:56:37 AKST
On 5 Dec 2001, Mac Mason wrote:
>
> I was benchmarking hard drives today, and found something interesting.
> I have hda and hde on a RAID-0.
> Hde is on a pci-based ata100 controller.
> now, with hdparm twiddled a little (-c 1 -d 1) I get the following:
>
> hdparm -t /dev/hda gives me 38.55 MB/sec
> hdparm -t /dev/hde gives me 9.04 MB/sec
> hdparm -t /dev/md0 (the raihdparm -t /dev/hdad device) gives me 18.71
> MB/sec
>
> Anyone else see my offboard drive cutting into my performance?
> So the question is twofold:
> First, I know that doing a mkraid hoses data. I don't want to hose my
> data, but I'd like to bring the 2nd HDD onto the motherboard controller,
> and see if that helps. Guess what, though: / is on /dev/md0. editing
> /etc/raidtab is easy, but how do I change the autodetection superblocks
> to the new drive letters without hosing it?
>
> Anyone have a link to a good set of pointers for hdparm, btw? I improved
> performace markedly by twiddling just a bit: I wonder if more could get
> me more.
I may be wrong, but you SHOULD just be able to update /etc/raidtab to
reflect the hde -> hdc (or whatever) change, shutdown, move the drive, and
fire it back up.
I think you would run into problems if, for example, you had a three drive
raid0 setup, and you swapped the positions of drives two and three.
In your case, because your two drives will still retain their relative
positions, you should be fine. However, it goes without saying to make a
good backup (and test it!) before you do it.
You should be fine though.
Mike
-- Mike Tibor Univ. of Alaska Anchorage (907) 786-1001 voice Network Technician Consortium Library (907) 786-6050 fax tibor@lib.uaa.alaska.edu http://www.lib.uaa.alaska.edu/~tibor/ http://www.lib.uaa.alaska.edu/~tibor/pgpkey for PGP public key
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