Use RAID1 mirror as backup during dist-upgrade?
I have a Debian Etch system that runs on a RAID 1 software raid system.
now I would like to upgrade it to Lenny by splitting the mirror off and
keep one mirror as a backup. Alternatively I could add a third disk as a
second mirror and split off this one.
If the upgrade works, I then add in the old disk again. If it fails I'd
like to be able to rebuild the array using the OLD mirror that I kept.
Does anybody have a more detailed description on how to do this? I know
I can fail a drive with mdadm, but my understanding is that the data on
this this drive can't then be used again after that. Is that correct or
can the bad upgrade disk be failed and then the old disk un-failed? How
would I tell the system which disk to use? What preparation steps are
necessary other than making both/all mirrors bootable?