NTFS is a perfectly good and happy filesystem. Some older OSes won't work with it, so you have to use FATx, but I have never heard of NTFS being slower even if it has the slight overhead of journaling (
http://en.wikipedia.org/wiki/NTFS#NTFS_Log ).
To the best of my knowledge... No, make that "No USB enclosure cares what filesystem is on the drive." It only provides a connection from the drive interface to a USB interface; the motherboard does the reading. (The exception is external RAID enclosures that do hardware RAID inside the enclosure, but that's not what we are talking about).
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Reformatting is a decent idea as long as you don't care about the data that is on it now. You might want to do one of three things based on the possibility that the disk is getting too old to use.
1) Go to Maxtor and download a utility to check the disk. See if it is showing signs of failure.
2) Attach the drive directly to the motherboard's EIDE port (if it has one) and see if the same behaviour persists, in which case you likely have a drive problem.
3) Just buy a newer drive.
4) Run a disk-speed test utility. USB is a pretty limiting interface; if you are getting full USB speeds then it's not the disk. The following is blatantly copied from Wikipedia, at this address:
http://en.wikipedia.org/wiki/Usb#Transfer_speeds_in_practice
Transfer speeds in practice
As of 2004[update], the actual throughput of USB 2.0 high bandwidth attained with a hard drive tested on a Mac was about 18 MiB/s, 30% of the maximum theoretical bulk data transfer rate of 60 MiB/s (480 Mbit/s). On Windows, the highest speed observed was 33 MiB/s, or 55% of the theoretical max. The drive could reach 58 MiB/s on Firewire, so the drive's speed was not a limiting factor.[56]
According to a USB-IF chairman, "at least 10 to 15 percent of the stated peak 60 MB/s (480 Mbit/s) of Hi-Speed USB goes to overhead — the communication protocol between the card and the peripheral. Overhead is a component of all connectivity standards."[57] Tables illustrating the transfer limits are shown in Chapter 5 of the USB spec.
Typical high bandwidth USB devices operate at lower data rates, often about 3 MiB/s overall, sometimes up to 10–20 MiB/s[citation needed]. A Full Speed device (for example PIC18f2550) easily reaches a little over 1MiB/s over a bulk endpoint[citati