[PLUG] Need mdadm help

[drew wymore]

On Sat, Dec 25, 2010 at 10:43 PM, John Jason Jordan <johnxj at comcast.net>wrote:

> Back in the days when Hardy was the reigning desktop distro I built
> myself a new desktop computer. I used two matching 320 GB drives and
> set them up as four partitions with RAID 1 (mirror) using mdadm. I wish
> I hadn't done that. Now I wish remove one of the drives, in effect, undo
> the RAIDs. Unfortunately it has been about three years since I created
> the RAID and now I can't make heads or tails of the mdadm man page. I
> must have been a lot smarter three years ago.
>
> Worse, I upgraded Hardy to Intrepid, and during the dist-upgrade the
> boot information was written to only one of the disks. I can boot, but
> only if I scroll down in the Grub menu and choose the previous kernel.
> Trying to boot to the current kernel gives me a Grub error 15. I have
> ignored this problem for a long time because the computer gets rebooted
> only if there is a power failure. This means that if I want to preserve
> the existing installation I have to figure out which partition (SDA1 or
> SDB1) has the correct boot information.
>
> There are four arrays:
>        SDA1 and SDB1 - 45 GB EXT3 boot and /
>        SDA2 and SDB2 - 2 GB swap
>        SDA3 and SDB3 - 20 GB EXT3 unused
>        SDA4 and SDB4 - 235 GB EXT3 old data, unneeded
>
> 1) For starters, how can I figure out the names I gave the arrays?
>
> 2) Once I know the names of the arrays I might be able to figure out
> how to remove one partition from each array, but how can I figure out
> which one (between SDA1 and SDB1) has the correct boot information?
>
> I hope someone can help me figure out what I did and how to change it.
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mdadm --query should be able to get you the array name at least if my
interpretation of the man page is correct. In terms of which device has the
correct boot information it might be a matter of trail and error, if you
unplug sdb and works then you know that logically it should be sda that has
the correct boot information.

Drew-