I've managed to set up my system with two drives, and RAID 1 mirror across them both so I am protected in case of a failure using the various howtos on this site. Many thanks for that. Now what I really want to do is use this setup as a backup for when I do upgrades etc. So when I'm about to do an upgrade I will split the mirror/fail one of the drives, and do the upgrade on the other drive. If the upgrade works I will then add in the old drive again. Unless anyone can see any issues I believe this is the easy part. However if the upgrade fails, I'd want to fail my current broken drive and add in the OLD backup disk. This is where I'm a bit unsure. Does failing a disk with mdadm make it useless, or is it still effectively a raid disk that can be used again? If so how would I rebuild the array against this. My other option is to power down, physically disconnect a drive, then do the upgrade. If it fails I'd then have wipe and disconnect the new broken drive and connect my old one, before adding the new clean drive. I dont see any issues with this working, but its a right pain opening and disconnecting cases. I thought this would be a common scenario but I'm struggling to find a decent howto. If anyone does it or has any idea how to fail and rebuild from a failed drive that would be very useful. Thanks in advance P.S. Not sure what category this should go in, so can the mods please move as required.