You seem to be under the mistaken impression that "RAID1" means *two* drives. It doesn't. It means one or more drives, all with exactly the same mirrored contents.

Eg. Commercial RAID vendors often use 4-drive RAID1 for data safety (and for faster read performance). All four drives are treated 100% equally.

So for the original proposal in this thread, it would be a *three* drive RAID1. Pull any drive out, and the system continues functioning. Pull a second drive out, and it still works fine.

Plug a removed drive back in, and the system will automatically resync it, while the other drives continue to work and provide full redundancy.

Mmm.. so I suppose what could be done here, is to initially create the RAID1 with all four drives installed, mirroring all of them together in RAID1.

Then remove one (or two, if you must) for off-site backup. The array will continue to operate, with full redundancy, but will claim to be "degraded" (missing a drive).

Later (days, months, seconds), pull out another drive to take off-site, and insert an original off-site drive as a replacement. The RAID array will automatically resync the inserted drive, provided it was one of the original RAID members.

No fancy scripts needed until you bring in a drive that was never part of the original RAID1 setup. Or at least that's how I remember it working, without actually configuring/testing it here today.

Cheers