Further paranoia: LVM and a decommisioned RAID member.

[Hendrik Boom <hendrik@topoi.pooq.com>]

On Wed, 18 Feb 2009 17:31:48 +0000, Hendrik Boom wrote:

> On Tue, 17 Feb 2009 18:22:43 +0100, martin f krafft wrote:
> 
>> also sprach Hendrik Boom <hendrik@topoi.pooq.com> [2009.02.17.1747
>> +0100]:
>>> But I understand these partitions are marked in some way to identify
>>> them as RAID members, and that these marks are used at boot time to
>>> asssemble the RAID.
>>> 
>>> What do I have to do to make sure that after I have removed the old
>>> member it is never again recognised as a RAID member?
>> 
>> There's a superblock. When mdadm starts, it scans the devices listed
>> for DEVICES in mdadm.conf (or all partitions if it says 'partitions')
>> for superblocks.
>> 
>> You can remove a superblock with --zero-superblock. See mdadm(8).
> 
> So the procedure would be somehtinglike:
> 
>    mdadm --fail /dev/md0 /dev/hda3
> to stop it from using /dev/hda3.  After this it should spend a happy
> hour copying the data on /dev/sda3, the other active drive to /dev/sdb3.
> the current spare.
> 
>    mdadm --remove /dev/md0 /dev/hda3
> to remove it from the set, and
> 
>    mdadm --zero-superblock /dev/hda3
> to make sure it never comes back.  Presumably I'm not supposed to
> mention /dev/md0 on this command because /dev/hda3 is no longer part of
> it.

Is that superblock the same one used by LVM to identify LVM partitions 
within the RAID?  Because if not at boot time =, LVM is going to detect 
all the LVM partitions both on the remaining RAID and on the 
decommissioned RAID member.  How will LVM know which volume is the real 
carrier for LVM paritions?

-- hendrik