From what you have described, sounds like a hard disk with bad blocks that only works "for a while" before needing a reformat. Try another 2.5" drive. I've not had any problems with 2GB+ drive partitions on my TAM, having had 40/60/and soon 100GB 2.5" drives installed with a single partition. I'm fairly sure it was the other way around with Woz's TAM - he was using a large HD without issues as well.