Woke up this morning, and my fileserver had emailed me this:
md0 : active raid5 sdh1[6](F) sdd1[5] sdc1[4] sdf1[3] sdg1[2] sdi1[7](F)
2441919680 blocks level 5, 64k chunk, algorithm 2 [6/4] [__UUUU]
Looks like I get a trial-by-fire of MD RAID recovery tonight, once I figure out what broke.