Re: Problems with USB Devices and RAID (And UUID) on Etch
On Wed, Feb 25, 2009 at 02:19:55AM -0500, Hal Vaughan wrote:
> I have an embedded server, so using SATA and internal drives is not an
> option. I've added 2 drives to this server and set up a RAID on it.
> These drives came from another system, used as a backup RAID there (it's
> got over 600 GB of data on it). I had hoped I could transfer them and
> just tell mdadm to find the drives and assemble the RAID on this
> computer, but there were several problems.
>
> When I started, the drives were /dev/sda and /dev/sdb. I had originally
> set them up, on the other computer, by using the entire drives and not
> partitioning them. This, and a few other issues, created problems, so I
> finally had to just reformat the drives using one partition, then rsync
> to transfer all that 600 GB of data BACK to this RAID (it took about 18
> hours to transfer that much data and restore it all!).
>
> I tried, when re-creating the RAID1, to specify the drives by UUID
> numbers:
>
> mdadm --create --verbose /dev/md0 --level=1 --raid-devices=2
> UUID=f5c49ce9-826b-43d5-9642-0189701e251f
> UUID=4c76d883-1b24-4195-bb67-a66e4503cab9
>
> but it didn't work and I had to do this:
>
> mdadm --create --verbose /dev/md0 --level=1 --raid-devices=2 /dev/sda1
> /dev/sdb1
>
> which worked fine. The RAID1 was created and I've got all the data back
> on it.
>
> I tried to specify these drives in /etc/mdadm/mdadm.conf with the UUIDs
> since I know the drives can change assignments between boots if they're
> USB. I can't specify them in that file -- I get error messages when I
> do.
>
> Now that the RAID1 is working, though, when I use vol_id to check the
> drives, they both show the UUID of the RAID1 device and if I try "vol_id
> --skip-raid /dev/sdb1", for example, both show the same UUID, the one
> above from sda1 (starts with f5...).
>
> I rebooted, after all the work was done, and had some trouble with the
> USB hub, but when it came up, the drives were /dev/sdb1 and /dev/sdc1
> and the RAID1 did not start at boot. It seems, with these drives on the
> USB hub, that they may not be active when mdadm starts.
>
> As I see it, I have a couple problems:
>
> 1) How do I make mdadm delay until the USB drives are all online?
A really ugly way would be to add your own custom script to the
initramfs.
Find the right directory under /usr/share/initramfs-tools/scripts , and
after you add your script rebuild the initramfs with
update-initramfs -u
Unless someone has a better suggestion.
> 2) How do I specify the drives to mdadm, since they both now have the
> same UUID and how would I do that anyway, since mdadm rejects "UUID=" in
> the command line and config file?
>
> It's also quite possible that there's something else going on that I
> don't see that could cause or solve problems, so if there's something
> else I need to look at, I'm open to it.
>
> Thanks for any answers, helpful suggestions, and so on.
>
>
> Hal
>
>
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