Abusing NetBSD's software RAID to make my backups has gone quite well. I have a draft of a document that describes what to do in all the common cases (adding a drive that's been used before, adding a drive that hasn't, and recovering files from backup). It's a short document, which gives me the same sort of feeling I used to get when finishing a math exam too early: have I missed something of urgent importance, or was it really that easy?

It really is that easy. NetBSD's software RAID maintainer likes the document.