Any chance that you found a solution for this?
Also, do we know if the system 'recreates' these files if we delete them? Does it recreate them upon use of the files? Upon webaccess of the files? I could maybe write a script to delete them...but I would hate to have to run it daily. I could just run it right before a big copy maybe. Or maybe I am breaking a lot by deleting them...who knows.
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My problem is related to the same hidden files. I don't do backups of my NAS, like you, but I do large photo folder copies from time to time that seem to grab these danged hidden thumbnail files.
Anytime I want to copy a folder of photos, it copies 7-8 times as many files as there are photos (they have them in .webview, .webaxs_L, _LL, _3L, _M, _S, and .thumbnail hidden folders. WTH Buffalo?!). These thumbnail files are small...but they add up. And when doing backups or copies, often total number of files is the speed limiter. Thousands of mini files that add up to 10gb take infinitely longer to copy than 10gb of 1gb files. Now if buffalo was smart and stored them in a system container rather than the actual file containers, then we would have less issues. A. you wouldn't have to deal with them on the daily with copies and backups, and B. you could just go delete a single large 'temp' file type directory full of these hidden thumbnail folders.
Last comment - I can only assume the system leaves remnant files as well in these thumbnail folders when I delete photos...