On Tue Oct 27, 2015 at 08:17:26AM -0400, Michael Munger wrote:

It's my understanding, that an array running with [UU_] is degraded and
there is a disk problem.

I have been trying to create a RAID array using this command:

mdadm --create --verbose /dev/md0 --level=5 --raid-devices=3 /dev/sdb1
/dev/sdc1 /dev/sdd1

However, once it create it, it get this in /proc/mdstat:

Personalities : [raid6] [raid5] [raid4]
md0 : active raid5 sdd1[3] sdc1[1] sdb1[0]
      3906764800 blocks super 1.2 level 5, 512k chunk, algorithm 2 [3/2]
[UU_]
      [>....................]  recovery =  0.1% (2611780/1953382400)
finish=1737.7min speed=18709K/sec
      bitmap: 0/15 pages [0KB], 65536KB chunk

I have done the following to "fix" the drive:

1. Smartmontools smartctl long and short tests. All passed.
2. Zeroed the first 1GB of the drive (overkill, I know I could just do
the first 512) with dd if=/dev/zero of=/dev/sdb count=250000 bs=4k
3. Re-partitioned the drive.
4. Re-create.

No joy.

Then, I swapped this hard drive out for another drive.

I am still getting [UU_].

Thoughts?

This is perfectly normal. A RAID-5 array is created in degraded mode,
then the final disk is synchronised. This makes the array available
immediately, with the synchonisation happening in the background.

Just leave it to complete the recovery process.

Cheers,
    Robin
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