On 14/07/2009 08:16, Ben Beuchler wrote:
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?
It'll work but you'll be using a legacy array without superblocks, so
you can't have various features that come with superblocks like being
recognisable or having a write-intent bitmap, which is why most guides
suggest you --create an array with a blank partition then copy the data.
The man page says of build mode:
Build an array that doesn’t have per-device superblocks.
For these sorts of arrays, mdadm cannot differentiate
between initial creation and subsequent assembly of an
array. It also cannot perform any checks that appropriate
components have been requested. Because of this, the Build
mode should only be used together with a complete under-
standing of what you are doing.
Cheers,
John.
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