When a backup fails to complete, that’s a reliable sign of trouble. Most of the time it’s in the backup mechanism, but the second most likely underlying cause is a problem in the thing which is being backed up.

(That’s all.)

This is a reminder that spinning storage is still useful for large data dumps, media, backups, and other bulky things that you don’t need to change continuously.

But mostly, it’s cost-effective. The two current sweet spots for capacity/performance (assuming brand-name, non-sale, 7200RPM SATA3 3.5" disks) are at 4TB (about $75) and 10TB (about $270).

I also remind you that you want RAID for reliability, but it’s not backup by itself.