Neil,

What seems desirable to me is a way to take a new (larger) spare drive and
add it to a RAID1 for a particular RAID 4/5/6 component, and then when
it's sync'd, replace the now redundant small drive with another larger
drive.  Wash, rinse, repeat.  This way the array is never degraded.
Though I imagine that this particular arrangement doesn't have the
benefit of the stripe rewrite when encountering a latent error on the
drive that is being migrated.  [Presumably the failing addresses could
be cycled through the check from userland though, by doing a read above
the stacked RAID.]

One could start a RAID 4/5/6 array over a degraded RAID1 for each
component, (i.e., a degraded RAID1).

I haven't been following the metadata changes closely.  Is it possible
to do this with external MD metadata?  It can also be done with
device-mapper, but dm-mirror is very immature compared to MD RAID1.

Comments?

Regards,

	Bill Rugolsky