not OP, but I tried to setup a NAS with my older B+, and it was really unreliable. The disk went to sleep every few minutes even when there was a file being read/written.
Fwiw, I don't remember having drive problems when I used a pi zero as a small NAS. I do remember configuring the drives to never idle and spin down, though. I think I used hdparm and I definitely had a power supply that could support the drives.
