This past winter, I was copying various huge media files to a portable 1TB drive formatted with NTFS, basically filling up the year's entertainment quota for my inlaws.
This was with a 2.5" 1TB WD notebook drive in a Vantec USB2-only enclosure.
All went well, albeit slowly, and I unmounted and sync'd the filesystems, and shut down the computer. The next morning, none of our computers could identify a useable filesystem on the drive.
I was not impressed by NTFS, but it's the only format their computers could read from when 4GB+ file sizes are involved. So I reformatted it, and copied back about 400GB of stuff AGAIN.
All was well, and nothing heard from again until this past weekend.
Months ago, they apparently had plugged the drive in, shuffled a few files around, added more, etc.. and then retired the drive for later viewing.
When we hooked it all up to the WDTV player for viewing on Saturday past.. nothing. No files, no filesystem, same as before.
The physical WD 1TB drive is fine. And my mistrust of NTFS may still be prudent, but that also wasn't the cause.. It's pretty much got to be the USB-SATA bridge chip inside the enclosure.
Most likely a 32-bit (signed) bug of some kind: Allowing for negative numbers ("signed") means one ends up with only 31 useful bits out of 32, which just happens to be the number of bits needed for keeping track of sector addresses on a 1TB drive.
That *should* be enough, especially since "1TB" in drive-maker-speak is really less than 1TB in powers of two. So one shouldn't expect that to be the issue, but perhaps they've also "stolen" one more bit for housekeeping purposes, leaving only 30 useful address bits.. max capacity 512GB.
I told my in-laws to toss the enclosure and let me get them a new known-good model from DealExtreme.
Beware.. though I'm not sure how one might "know" any better.