From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ben Beuchler <insyte@gmail.com>
Subject: migrate single disk to RAID 1?
Date: Tue, 14 Jul 2009 02:16:40 -0500
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I'd like to convert an existing partition to RAID 1 using a portion of
a new, blank drive.  All of the examples I've seen involve creating
the RAID device with the *empty* partition (sda4), copying the data
from the old partition to the new RAID, then adding the old partition
to the RAID set.

>From my modest understanding of how linux software RAID works, it
seems I should be able to take an existing partition containing data
(in this case sdb4 mounted as /mail) and build a RAID 1 array with
something similar to this:

umount /dev/sdb4
mdadm --build /dev/md0 --level=1 -n2 /dev/sdb4 missing
mount /dev/md0 /mail
mdadm --add /dev/md0 /dev/sda4

Will that work?  Or am I misunderstanding something fundamental?

Thanks!

-Ben