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Old 06-03-2007, 03:45 PM   #1
Registered: Feb 2007
Posts: 32

Rep: Reputation: 15
How do I resync a "dirty" software raid1?

I have a software raid 1 array here, consiting of two drives:
sudo mdadm --create /dev/md0 -a -l 1 -n 2 /dev/sdb /dev/sdc

To test it I pulled out one disk, made changes to the ramining disk and then plugged back in the other drive.

I ended up with:
  md0 : active raid1 sdb[0] sdc[2](F)
      488386496 blocks [2/1] [U_]
Which - as it seems - the system does not automatically resync. Now, how do I tell the system to re-accept the reappeared drive sdc and sync it up with sdb?

For further description of my problem and how I ran into it, please read:
Old 06-03-2007, 04:04 PM   #2
Registered: Jan 2005
Location: germany
Distribution: suse, opensuse, debian, others for testing
Posts: 307

Rep: Reputation: 32
you need to remove the failed/missing device with mdadm first and the re-add it to start the rebuild/sync.
mdadm --manage /dev/md0 --remove /dev/sdc
mdadm --manage /dev/md0 --add /dev/sdc
you could have tested it without actually pulling a disk. mdadm can "software-fail" a device with

mdadm --manage /dev/md0 --fail /dev/sdc
Old 06-04-2007, 01:12 AM   #3
Registered: Feb 2007
Posts: 32

Original Poster
Rep: Reputation: 15
Thanks a LOT!
That did it.

Actually I got a
hot remove failed for /dev/sdc No such device or address
first, which brought me to

As it seems re-booting/waiting during the process made mdadm remove the drive completely from the array during the process. So, when I tried to "--remove" it, it was in fact already gone. So
sudo mdadm /dev/md0 -a /dev/sdc
did the trick!

And when resync was slow (7000min! on a non-production machine) I did "sudo -s -H" to circumvent the ubuntu “permission denied” problem and then "echo 50000 >/proc/sys/dev/raid/speed_limit_min" - and instantly I was down to 240min.

Now my last question: Should I worry about fdisk giving
sudo fdisk -l /dev/sdb
Disk /dev/sdb doesn't contain a valid partition table

Last edited by isync; 06-04-2007 at 01:36 AM.


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