REPAIR TABLE rebuilds the entire table and index, so you'll need to have enough diskspace. The error 9 is probably mysql running out of space during the rebuild. You won't notice it after because it discards the temp files.

You'll need table size + index size + extra to do a full repair. Also, because mysql doesn't run as root, you won't have your entire disk available for the repair (if you're running Linux on ext2 or ext3) because of the reserved blocks. Check tune2fs's manpage for more info on those...

I've worked with 80Gb+ tables more then I care for, and have run into this sort of issue way too often...