Folder problems on external drive, not showing correct file size

Question

I've run across a strange problem. I'm media managing for a tv show, meaning I'm offloading video from CF cards onto 2 external drives, one is a Drobo Raid (set up for backup) and another is a Lacie rugged drive. After copying the media to both drives, the folder I copy will match, but sometimes as I drill upward in my folder structure, suddenly the file sizes will not match. To be more clear: 2 folders will show differing file sizes, but inside that folder is only another folder,nothing else, which matches across the drives. I've shown all files in finder and there's no hidden files, though sometimes I see the ds_store files are different sizes (8k vs 16k), but that's not always the case. Sometimes if I simply create a new folder and move it's contents into it I can get the folders to match, but sometimes that doesn't work. It's part of my workflow to show that these copies match exactly via screenshots, and although the most important folder (the direct folder holding the footage) always matches, these folder problems are super frustrating as it's not constant, and any workarounds also work inconsistantly.
I had an accidental disconnect of the Drobo one time, and although none of the data seems to have any problem, I fear it's done something to the directory. The rugged drive is swapped out every few days and the problem seems to be on the Drobo. Because the nature of the data is pretty important, I'm afraid to just try messing around with repairing or other software solutions unless I know it's super safe and won't harm the data.
I'm at a loss as to what's causing it and at the very least how to avoid it cropping up. Any help or insight would be appreciated!

Answer 1

I had the same problem with my iMac, first I repaired the disk, then I ejected the disk, restarted, and then reinserted the USB in a different port.  All of my files magically showed up.  I don't know what caused the error but it has been working fine since.