OS on 50GB partition on 750GB Seagate SATA drive, rest of drive used for storage (D drive). Drive is old - at least 3 years but possibly up to 5.
Started having problems watching shows recorded on the D drive (I have 2 other drives also used for storage and 2 external for backup and their speeds were fine). No changes had been made to system for some time.
Also noticed slowdown when an Adobe update was being installed.
Ran diagnostics which were slow but no errors.
Ran ATTO and speeds were ridiculously low (2Mbps).
Tried reformatting the D partition and aligning but made no difference.
Replaced drive with a WD 750 drive (old one I kept as spare) and speeds were back up to normal. OS partition was copied from problem Seagate drive.
Put the problem Seagate drive in another system to test and the speeds were back to normal.
Would have chalked it off to bad drive if it hadn't run well in the other system.
Scratching my head over this one. Any explanations would be appreciated.