On my MBP, I installed an SSD as my main drive and moved the HDD to the optibay. The HDD was formatted with NTFS, and I intend to save mostly media files here and be accessible by Windows (via Boot Camp) and OS X. I access the NTFS partition on the HDD only occasionally, but it doesn't spin down if the NTFS for Mac driver is on. My MBP loses battery faster. - I tried setting "Disable Last Access Time" on the drive but it still has the same behavior. - There are no other processes accessing the drive--I verified using the "sudo fs_usage | grep name_of_volume" command. - If I disable the driver, unmount then mount back the partition, the drive spins down after a period of inactivity. This pretty much means NTFS for Mac is doing something on the drive and not letting it spin down. Thoughts? Any fixes?