I use a wifi controlled powerpoint to power up and down a pair of raid1 backup drives.
A weekly cronjob on another (always on) machine does some simple tests (md5 checksums of "canary files" on a few machines on the network) then powers up and mounts the drives, runs an incremental backup, waits for it to finish, then unmounts and powers them back down. (There's also a double-check cronjob that runs 3 hours later that confirms they are powered down, and alerts me if they aren't. My incrementals rarely take more than an hour.)
I think I'm missing something.