My backup strategy is in two parts: Internal backup and external backup.
My first line of defense is an internal Time Machine drive that backs up my entire system automatically. This is a rolling backup that tracks all changes going back about six weeks.
My second backup is a pair of extrnal hard disks to which I back up once a month. But I do not use external enclosures. I used
bare drive mechanisms.
Why not use external drive enclosures? Cost and convenience. I have purchased a number of expensive external drive enclosures over the years, and have found that the pace of technology makes them a little too disposable for my taste. So, I now use a $30 SATA-to-USB adapter cable and plug the bare drive directly into the computer's USB port.
I then store the drive mechanisms in one of these cases:
Pelican™*Products*1300*Case
The case is full of cubed foam, cut to match the shape of the drives precisely. The case is airtight, water titght, and extremely tough. I store the case off-site as a hedge against unforeseen disaster.
And when I need additional storage, I just buy another drive mechanism, and carve out a new slot in the foam. Much less expensive and troublesome than external FireWire or USB enclosures.
I would have preferred my adapter cable to go from SATA to FireWire 800, but the costs of those adapters is obscenely high.
Hope all that helps.