[SATLUG] CentOS installed to external USB 2.0 RAID1 drives = frustration

[Sean Carolan]

> What do the boot stanzas in your grub (or lilo) menu say? Here's the one
> from grub I use with a root-on-RAID system:

All right, I thought I had this squared away but found that it's not
completely working.  Here's the problem I'm faced with now:

/dev/md1 = /home  (works fine)
/dev/md2 = swap (also works fine)
/dev/md0 = / (only loads /dev/sdb1, not /dev/sda1)

Here are some diagnostics if it's of any help:

Output of cat /proc/mdstat:

Personalities : [raid1]
md2 : active raid1 sdb2[0] sda2[1]
      1052160 blocks [2/2] [UU]

md1 : active raid1 sdb3[0] sda3[1]
      103876224 blocks [2/2] [UU]

md0 : active raid1 sdb1[0]
      12289600 blocks [2/1] [U_]

unused devices: <none>

Output of "mdadm -D /dev/md0"

/dev/md0:
        Version : 00.90.01
  Creation Time : Thu Mar  1 02:12:02 2007
     Raid Level : raid1
     Array Size : 12289600 (11.72 GiB 12.58 GB)
    Device Size : 12289600 (11.72 GiB 12.58 GB)
   Raid Devices : 2
  Total Devices : 1
Preferred Minor : 0
    Persistence : Superblock is persistent

    Update Time : Thu Mar  1 22:40:30 2007
          State : clean, degraded
 Active Devices : 1
Working Devices : 1
 Failed Devices : 0
  Spare Devices : 0


    Number   Major   Minor   RaidDevice State
       0       8       17        0      active sync   /dev/sdb1
       1       0        0       -1      removed
           UUID : 941896b1:4cd2bf1d:2d320d1d:3a7867cb
         Events : 0.921

What happens when I try to add /dev/sda1 to the array:

[root at localhost ~]# madm /dev/md0 -a /dev/sda1
md: could not bd_claim sda1.
md: error, md_import_device() returned -16
mdadm:hot add failed for /dev/sda1: Invalid argument

I tried to fsck on /dev/sda1 but the system thinks it is mounted!  I
tried the mount command and checked /etc/fstab and this does not seem
to be the case.

Any ideas? I have no idea what to do at this point.  I've been
googling around for hours trying to find someone with the same
problem, but to no avail.