Mirroring Entire Drives Partition Type Clarification

[Jared Raddigan <jraddigan@kfh.org>]

Playing with mdadm today I noticed it seems to allow full drive
mirroring something I remember that raidtools would fail on.

 Back in raidtools days I remember that even though it was possible to
mirror an entire drive with a single md volume (sda, sdb rather than
sda1, sdb1) it really did not work and was not recommended.  It looks
like that is no longer the case with mdadm.   Here is what I did.

 Took two hard drives and created a single partition that spans the
whole drive.  then do:

 mdadm --create --level=mirror --raid-devices=2 /dev/md1 /dev/sd[ab]1

 Look using mdadm --detail and see
 Number   Major   Minor   RaidDevice State
        0       8        1        0      active sync   /dev/sda1
        1       8       17        1      active sync   /dev/sdb1


 I reboot and now using mdadm --detail I see:
 Number   Major   Minor   RaidDevice State
        0       8        0        0      active sync   /dev/sda
        1       8       16        1      active sync   /dev/sdb

 So it would seem mdadm basically figured out what I wanted to do and
no longer shows the partition number after a reboot.  So next deleted
all partitions on the drives and recreated the raid set without
referencing the partitions

 mdadm --create --level=mirror --raid-devices=2 /dev/md1 /dev/sd[ab]

 That worked just fine and now  mdadm --detail gives me the same as
before (but without rebooting)
 Number   Major   Minor   RaidDevice State
        0       8        0        0      active sync   /dev/sda
        1       8       16        1      active sync   /dev/sdb


 My questions are:

 Is there anything wrong with doing this as this was not recommend
with raidtools.  This with LVM or partition the md directly (cool
feature you added) seems like a hard combo to beat?

 Does the MBR get synced across the drives when doing this?

 I know partition type does not seem to matter with mdadm compared to
raidtools, but when creating partitions I use "da" rather than "fd",
is that the recommended type or since it no longer seems to matter no
one really cares what you use?

 I am using version mdadm - v2.6.7.2 - 14th November 2008 from Debian Lenny

 Thanks and I am pretty excited how mdadm keeps getting better and better.

 --
 Jared


>
>



--
Jared Raddigan
Koinonia I.T. Director
p. 916-577-7982 x101
http://www.kfh.org
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html