Do not split a RAID array across drives in separate USB enclosures.

Doing RAID on USB drives is alright, as long as they’re all in the same enclosure and use a single USB interface. If you split an array between drives with separate USB interfaces, you will face corruption and rebuild issues when one of the controllers has a hiccup or comes up slower/faster than the other, which WILL happen. If you need to run a RAID array on USB-connected drives, use a 2-bay USB-connected DAS. I’ve used the QNAP TR-002 in the past, it works fine, just set it to individual mode.

The better option since we’re just talking about a mirror, is to run on one drive primarily, and occasionally sync your data to the other for a backup.

4-bay DAS with a handful of big HDDs in RAIDZ1. Load it up, then store it in your office at work or at a friend or family member’s house. Retrieve, update, and scrub somewhere between once every few weeks to once every few months, depending on how often your critical data is changing.

The hard links aren’t between the source and backup, they’re between Friday’s backup and Saturday’s backup