My HFS+ formated USB 3 direct connected drive (no hub) spins down during iTunes playback and the only remedy is to disconnect/reconnect the drive cable.
STAC10000301 1Tb model, Mac OS X 10.7.4 running Seagate Diagnostics Version 1.1.3 Driver version 5.1.1
It seems to behave OK in apps other than iTunes though not 100% of the time as I've had occasions where it has stopped when iTunes is not running. They are hwoever few and far between compared to when iTunes is there.
Reading the many, many posts on OS X incompatibilities with Seagate drives I'm thinking continuing to search for an answer is an exercise in futility despite the claim they are OS X compatible.
My Lacie drive is now on order and the Seagate relegated to the pile of Windows only junk.
If however anyone has a silver bullet solution, please feel free to share.