I have noticed some strange behavior from both of my 2TB Hitachi 7200RPM drives, which are currently inside external Nexstar3 USB3.0 cases. They are manually mirrored for file redundancy.
Whenever I copy over a bunch of small files, or something relatively small, like around 100MB or so, the file progress bar under Win7 x64 displays correctly; it gradually advances to the right until it's complete.
But when I copy over larger files, like a single 350MB file for example, the progress bar will instantly shoot up to 90% complete, then stay there for the entire time until the file is done copying, at which point it will finish and the box will disappear. This occurs on both drives.
There is nothing wrong with the drives operationally, but this is a concern because I haven't noticed this behavior on either of the two 500GB drives I own. Why is this happening, and is there anything I can do to fix them?
Windows was never very good at accurately calculating transfer times. It could be a Windows bug or it could be that USB 3.0 drivers aren't fully mature yet. Could be any number of things. I wouldn't worry about it, as long as the files are copying successfully.
Windows caches file reads and writes. If you're copying a file that's already in the cache (one you've just downloaded, for example), then it won't have to wait for the disk to read the source file, and it will cache the writes to the target file in RAM. The result is that the first part of the transfer will appear to go very quickly. But if the copy is too large to completely fit in RAM then the transfer will appear to slow down to the actual speed of the disk while the rest of the data is dumped from the cache.
I'd have to agree...the OS can only really try to estimate...as stated, it's much easier on smaller copies. You could use other copy programs, which I have found are quite a bit more accurate - teracopy is a favorite.