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I'm running CentOS 6 x86_64. There is a software RAID 1 being used on the two internal 80GB drives. I got the following e-mail sent to me:

A DegradedArray event had been detected on md device /dev/md1.

Faithfully yours, etc.

P.S. The /proc/mdstat file currently contains the following:

Personalities : [raid1]
md0 : active raid1 sda1[0]
      511988 blocks super 1.0 [2/1] [U_]

md1 : active raid1 sda2[0]
      8190968 blocks super 1.1 [2/1] [U_]
      bitmap: 1/1 pages [4KB], 65536KB chunk

md4 : active raid1 sdc1[0] sdb1[1]
      1953512400 blocks super 1.2 [2/2] [UU]

md3 : active raid1 sdd5[1] sda5[0]
      61224892 blocks super 1.1 [2/2] [UU]
      bitmap: 1/1 pages [4KB], 65536KB chunk

md2 : active raid1 sdd3[1] sda3[0]
      8190968 blocks super 1.1 [2/2] [UU]

unused devices: <none>

The system appears to have booted fine and is working.

The two drives' content did not change at all. I only removed and reinstalled them while I was booted on the CentOS Live DVD.

How do I get the array working again?

share|improve this question
So you removed part of a mirror. Worked on the system (thus changing the contents of the non-removed mirror drive). Then put the old drive back and you are surprised that the contents do not match and that the computers complains about it? – Hennes Oct 22 '12 at 14:00
I didn't change the two drives at all. I only removed them, and re-installed them as I said. I didn't change the contents of them at all. The other devices weren't even powered on, I was running from CentOS DVD-ROM to test them out. Now, do you have something constructive to add for me to fix this? – Edward Oct 22 '12 at 14:24
I read the OP as I removed two drives of a two different RAID sets. Then did stuff with other disks, then put the disks back. With your edits to the OP it now makes more sense. – Hennes Oct 22 '12 at 15:03
Even after the update, it's still confusing. I don't think there's any need to add "UPDATE:" when you can directly edit the post so that it is more clear. – gparent Oct 22 '12 at 15:49
The same thing Hennes is mentioning. He's entirely right, your question leads one to think that you wrote on the non-removed mirror drive. Quoting Roosevelt won't change that. – gparent Oct 22 '12 at 15:52
up vote 6 down vote accepted

When you pulled out the drives from your running system, you broke the mirrors.

Re-add the appropriate partitions to your failed mirrors:

mdadm --manage /dev/md0 --add /dev/sdd1
mdadm --manage /dev/md1 --add /dev/sdd2
share|improve this answer
Thanks, MikeyB! – Edward Oct 22 '12 at 15:51

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