On Thu, 15 Jul 2010 11:50:56 +0200
"Ceuleers, Jan (Jan)" [off-list ref] wrote:

Neil,

quoted

mdadm -A /dev/md2 --force /dev/sd[ade]2

Many thanks for your feedback. I will try this when I get home.

So if I boil this down to the principles, your advice is to assemble
the array in degraded mode using the components that have the most
recent update timestamps. Degraded, because this prevents
resynchronisation.

It is more a case of "degraded because that uses fewer devices, and
so fewer old devices which could introduce errors."  though avoiding
resync is a good thing too.

The key bit is "--force" which tell mdadm to assemble it anyway
even if something looks out of data.  mdadm will only include just
enough devices to make the array work.
You don't really need to be selective about the devices you
choose. If you give "mdadm -Af" all of the devices, it will just
pick the ones that are best.  I just listed them for you to
make it more clear what was happening.

NeilBrown