With disk usage on my main fileserver hovering around 98% after a weekend of recording and a week of editing, it was clearly time to Do Something. And this particular something has been planned for a while.
About a week ago I thought to check, found the "etch-and-a-half" (2.6.24) kernel, and installed it. It seems to completely fix the mysterious hang-up on long writes that's been plaguing me for a year on 2.6.18, so I was finally able to move the Debian mirror off the fileserver and onto the gateway machine, where a 175GB partition has been waiting for just such an occasion.
With 100GB moved, the fileserver is down to 71%; the gateway stands at 68%. So I get to keep my 500GB disks for a while longer; hopefully until 1TB gets under $100.
Adding to the excitement, I found that my mirror hadn't actually been updated since January sometime, when I cleverly renamed the administrative user (because admin is taken now) without renaming its crontab. Oops. All better now.
I've also put in some work on the Tres Gique website.