> How do I tell if my external drive uses NTFS?
1. Open Terminal app ( in Applications > Utilities )
2. Type in diskutil list and Enter.
3. You will see lines of output something like below. ( This is for my Mac Mini with Internal drive only )
/dev/disk0
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *1.0 TB disk0
1: EFI EFI 209.7 MB disk0s1
2: Apple_HFS Macintosh HD 999.3 GB disk0s2
3: Apple_Boot Recovery HD 650.0 MB disk0s3
You will get second set of similar following them for (most likely) /dev/disk1, if your mac has an external drive connected.
In the case above, there are three partition. - EFI (for mac boot), Macintosh HD (OS X), and Recovery HD ( for booting in recovery mode ).
The TYPE column tells what is the format of the partition.
- "Apple_HFS" is for normal boot/data partition for OS X.
- "Microsoft Basic Data" is NTFS, for Windows data or boot , including BootCamp.
Other possible TYPE can be listed with another Terminal command diskutil listFilesystems.
> I couldn't even read from the drive when I plugged it in.
I can only guess, as I have no detail info about what happened on your Mac at this point.
Probably, the Seagate driver took over OS for NTFS handling, but it fails to process due to necessary software ( part of driver ) did not work properly due to the compatibility with Yosemite.
It may help to identify the problem if you can find error messages in system log, which can be viewed with Console app ( also in Utilities folder ).
The message may come out either at OS boot or on connecting the drive.
Also, visit Seagate site and check if any firmware update is available for your drive ( req. serial number ).