Re: How to grow RAID1 mirror on top of LVM?

[Russ Hammer <russ@perneus.com>]

On Sun, 2008-05-04 at 21:20 +1000, Neil Brown wrote:
> On Friday May 2, russ@perneus.com wrote:
> > 
> > My plan basically was:
> > 
> > # remove one small disk
> > /sbin/mdadm /dev/md0 --fail /dev/sdb1
> > /sbin/mdadm /dev/md0 --remove /dev/sdb1
> > 
> > # shutdown and swap in large disk
> > # (with larger partition for the RAID1 component)
> > # add large drive into array
> > /sbin/mdadm /dev/md0 --add /dev/sdb1
> > 
> > # Allow the array to resync
> > # remove the remaining small drive
> > /sbin/mdadm /dev/md0 --fail /dev/sda1
> > /sbin/mdadm /dev/md0 --remove /dev/sda1
> > 
> > # Grow the array
> > /sbin/mdadm -G /dev/md0 -z max
> > 
> > # shutdown and swap in second large disk
> > # (with larger partition for the RAID1 component)
> > # add in the second large drive
> > /sbin/mdadm /dev/md0 --add /dev/sda1
> > 
> > My concern (based on this discussion) is that this will fail because I
> > am changing the size of the partition underlying the RAID1 array, much
> > like the LVM discussion above, while using ver 0.90 superblock.
> > 
> > Do I have a legitimate concern??
> 
> Your recipe is perfect.  You need not be concerned.
> 
> You are *not* changing the size of the partition underlying the RAID1
> array.  When you change the size of a partition, it is not part of the
> array at that time.  It has no superblock on it, so there is no room
> to be confused.
> 
> If you were to make a small partition on the new sdb, add that to the
> array, then change the partition table to make sdb1 bigger, that would
> cause confusion.
> However as you are making sdb1 nice and be before including it in the
> array, everything should work perfectly.
> 
> The only possible problem area in your recipe is if the drives are not
> actually identical (not all 750GB drive have the same number of
> blocks), the array you get with the -G command might be too big to
> allow the partition you create on the new sda.  However if the drives
> do have exactly the same number of sectors, this will not be a problem.
> 
> NeilBrown

Thanks, I see the distinction now.

Russ