Problems with USB Devices and RAID (And UUID) on Etch
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?
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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