Re: Reuniting disks in a raid1 array

[Lars Noodén <lars.nooden@gmail.com>]

On 08/30/2016 08:33 AM, Frédéric Marchal wrote:
>...
> Now, it's time for the old computer to retire and sdb to join its partner in 
> the new raid1 on the new computer.
> 
> How can I do this safely?

Here is what I did when I restored a drive to a RAID 1 array.  I'm not
an expert, so you'll want to verify these steps.

First I cleared the start of the drive-to-be-added using "dd" reading
from /dev/zero for 1MB (probably unnecessarily large).  Then I copied
the partition table from the existing disk in the array to the
disk-to-be-added.  I used a different method, but looking around the
correct way might have been to pipe output from "sfdisk -d" on the
existing drive to  "sfdisk" on the drive-to-be-added.  That put the
partition(s) in the right place(s).  Then I added the "new" RAID
partition to the array using "mdadm".  e.g.

	mdadm --add /dev/md129 /dev/sdb3

Then it was just a matter of waiting and checking.  e.g.

	mdadm -D /dev/md129

When it was finished, it showed that it was again clean and that both
devices were present and in use.

          State : clean
 Active Devices : 2
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 0

YMMV

Regards,
Lars