Do any guru-types out there have any idea if it's possible to tell Myth (.18, if it matters) to store recordings to more than one hard drive? My main myth drive is about 60 gig, which doesn't store terribly much video.

I can move the .NUV files and play them manually, or transcode to save space, but I'd really like to be able to tell it that when it runs out of space on /myth, it should just start dropping them into /overflow (or whatever). I had thought it might be possible to make the filesystem automagically make two partitions (or two separate physical drives) appear to be one -- sort of a software RAID-0, only I don't care if the files are actually striped or not, and I'd like to be able to use all the space on two different-sized partitions. If that's possible, I haven't figured out how.

Alternately, it would be fine to have e.g a cron job to move old shows over to a different drive, but I'd like it if there could somehow be an automatic update so the database still knows where to go to get them. My script-fu is not strong enough, sadly. So, if anybody has run into this and found themselves an easy out, please do let me know. If I figure one out for myself, I'll post it here.

You need to use LVM to span 2 partitions, there is a howto on the wiki i believe.