[ubuntu] How to recover directories that spontaneously vanished?

OK, please bear with me...

I've got this 1TB exteal USB hard drive, NTFS formatted, and it's on an old netbook that I leave ruing 24/7 for P2P filesharing with Transmission. The netbook runs an older version of the Crunchbang Linux distro (now BusenLabs Linux). Anyway, on the 1TB drive I have a top-level directory called "TRANSMISSION_EXTERNAL" under which I have (had) a separate directory for each torrent in order to stay organized. I.e.: inside "TRANSMISSION_EXTERNAL" there'd be a folder for "TORRENT_1" which would contain both the torrent (pointer) file and the file data for that torrent (being shared). I don't use the netbook for anything else: often I don't touch it for weeks at a time and just let Transmission do its thing.

I like to seed old/hard-to-find stuff, so I tend to leave torrents ruing for a long time. There are (were) a few hundred different torrents ruing, and thus, a few hundred sub-directories inside of the "TRANSMISSION_EXTERNAL" directory. Until one moing the other week, when I glanced at Transmission to see that it was reporting that hundreds of the ruing torrents were erroring because it now couldn't locate the relevant directories. I kid you not: about 95% of all the sub-directories inside of "TRANSMISSION_EXTERNAL" had vanished: they were nowhere to be found on the drive: not in Trash, or when viewing hidden files, etc... Only 31 directories remained of the hundreds that were there a day earlier.

I have no idea how or why they disappeared (a bug in Transmission? a gremlin in Crunchbang?) and am unable to find the missing directories (and the files they contain) but I think they're still on the drive because about 197GB of space is unaccounted for, as if stuff had been deleted but the space it used hasn't been freed up for re-use yet. Attached is a screen cap of Properties for the 1TB drive... as you can see, the current contents only account for 54GB of space, but 251GB is being "used" ...there's 197GB worth of stuff someplace that I can't see/find: that should/could be the vanished directories and their files.

1TBdriveproperties.png

In addition to searching the entire drive for known filenames, with Show Hidden Files tued on, I looked inside the ".Trash-1000" sub-directories and they only contain a few recent, manually-deleted files: NONE of the missing directories are in there. Nor are they to be found in the "$RECYCLE.BIN" or "System Volume Information" directories (that show up with Show Hidden Files; please see attached screen cap).

1TBcontentsshowhiddenfileson.png

Can anyone suggest a way that I could locate the 197GB worth of vanished directories that I suspect/hope are still intact somewhere on the drive? Maybe there's a file utility that would help? I've been careful to use the 1TB drive as little as possible to avoid accidentally overwriting the missing data. I've got the drive coected to my main PC now (ruing Ubuntu 14LTS) and would be *extremely* grateful to anyone who could tell me how to recover/salvage the missing directories if possible. Thanks in advance.