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3 Replies Latest reply: Sep 27, 2012 12:42 PM by Dude! RSS

Issue with MD mirror

bobthesungeek76036 Pro
Currently Being Moderated
I inherited a Scientific Linux 6.2 system that had a triple mirror for it's OS device; sda, sdb, & sdc. I tried to remove sdc from the mirror using:

<pre>
mdadm --fail /dev/md0 /dev/sdc1
mdadm --remove /dev/md0 /dev/sdc1
</pre>

but the device md0 shows degraded:

<pre>
# mdadm --detail /dev/md0
/dev/md0:
Version : 1.0
Creation Time : Fri Jul 20 07:38:36 2012
Raid Level : raid1
Array Size : 511988 (500.07 MiB 524.28 MB)
Used Dev Size : 511988 (500.07 MiB 524.28 MB)
Raid Devices : 3
Total Devices : 2
Persistence : Superblock is persistent

Update Time : Tue Aug 28 16:25:57 2012
State : clean, degraded
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0

Name : localhost.localdomain:0
UUID : 8b68d22d:4566147a:621a50a4:6d016578
Events : 325

Number Major Minor RaidDevice State
0 8 1 0 active sync /dev/sda1
3 8 17 1 active sync /dev/sdb1
2 0 0 2 removed
#
</pre>

I did the same thing with md1 and it too is in the same state.

mdadm.conf looks like this:

<pre>
# mdadm.conf written out by anaconda
MAILADDR root
AUTO imsm 1.x -all
ARRAY /dev/md0 metadata=1.0 level=raid1 num-devices=2 UUID=8b68d22d:4566147a:621a50a4:6d016578
ARRAY /dev/md1 metadata=1.1 level=raid1 num-devices=2 UUID=b2bc5b0b:4d3a33ba:39e6a2fb:be3ae14c
</pre>

Is there any way to clear up the degraded state of these MD devices? I tried zero-superblock but it didn't work:

<pre>
# mdadm --zero-superblock /dev/sdc
mdadm: Unrecognised md component device - /dev/sdc
# mdadm --zero-superblock /dev/sdc1
mdadm: Unrecognised md component device - /dev/sdc1
#
</pre>
  • 1. Re: Issue with MD mirror
    Dude! Guru
    Currently Being Moderated
    If you check the mdadm detail output:

    Raid Devices : 3

    Apparently the software RAID in your configuration was created with 3 devices. 1 is missing and hence the RAID set is degraded. You will have to reduce the number of devices that are registered in the RAID set.

    After failing and removing the drive, which you already did, I suggest the following:

    <pre>
    mdadm /dev/md0 grow raid-devices=2 --backup-file=/boot/md0.backup
    </pre>

    Since 2 disks are good enough for a RAID 1, --backup probably won't do anything.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
  • 2. Re: Issue with MD mirror
    bobthesungeek76036 Pro
    Currently Being Moderated
    Dude! You are my hero!!! Thanks!!! Worked like a charm!
  • 3. Re: Issue with MD mirror
    Dude! Guru
    Currently Being Moderated
    Btw, if you use "blkid" utility, the device will still be listed as type "linux_raid_member". After the device has been removed from the RAID set, you can erase it, for instance:

    <pre>
    # mdadm --zero-superblock /dev/sdc1
    </pre>

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