Max Waterman wrote:

Of course, you could always *not* yank them; instead just fail them
(after unmounting/syncing/whatever) and leave the actual disk in the
machine.

Also worth mentioning is that you can have a 3-way RAID1.

So adding a disk, allowing it to sync and then removing it again means you are
never left with just a single point of failure.

You can of course send the 'backup' disk(s) to sleep too.

David