I'd recommend ZFS for working with these kind of arrays; scrub is a command that's easy to regularly schedule, and will only use idle I/O bandwidth (helps that the RAID functionality is integrated with the whole filesystem).

If you have an infrequent scrub policy and hit bad sectors on rebuild, it can detect checksum failures and mark specific files as corrupted, rather than declaring all your disks defective. Traditional linux md raid behaviour is particularly bad in this regard: if you have a raid6 configuration and haven't been scrubbing, and then have a single disk failure, all your disks will have a few random isolated bad sectors (i.e. sectors that will URE when you attempt to read them) on, but since you still have one disk's worth of parity it's possible to recover all your data with no downtime (and with ZFS raidz2 this is what would happen). But with md raid as soon as you hit those bad sectors during the rebuild it will consider those drives as failing and kick them out of the array, and since all your drives have at least one bad sector on that means it's impossible to recover the array.