Hi and welcome to TSG.
First thing to remember is pretty much all harddrives fail at some point, its not a case of 'IF' its a case of 'WHEN'?
You say the drive is almost full, how full as a percentage? If the drive is almost full this could significantly impact performance.
If it is failing you need to get the data off if you want to save it. Personally, I would start copying the data off ASAP. If it fails while you are taking data off at least you have saved some of it, if it fails while your 'testing' you could loose everything!
Seatools can be used to test the drive in DOS or Windows (dependant on the version), this is a utility by Seagate for testing their drives.
http://www.seagate.com/gb/en/support/downloads/seatools/
This should give you a definitive answer or at least a good indication if there is a problem with the drive. For a 3TB drive it can take quite a bit of time to test, even more so if the drive has very little free space.
First thing to remember is pretty much all harddrives fail at some point, its not a case of 'IF' its a case of 'WHEN'?
You say the drive is almost full, how full as a percentage? If the drive is almost full this could significantly impact performance.
If it is failing you need to get the data off if you want to save it. Personally, I would start copying the data off ASAP. If it fails while you are taking data off at least you have saved some of it, if it fails while your 'testing' you could loose everything!
Seatools can be used to test the drive in DOS or Windows (dependant on the version), this is a utility by Seagate for testing their drives.
http://www.seagate.com/gb/en/support/downloads/seatools/
This should give you a definitive answer or at least a good indication if there is a problem with the drive. For a 3TB drive it can take quite a bit of time to test, even more so if the drive has very little free space.