Why do I have duplicate file names prepended with "._" ?

[Art G.7]

In all or most of my folders, my file names are duplicated but with a period-underscore "._" appearing before each duplicate.  The duplicates don't open to anything except "This file type can't be viewed". 

This may have come about when I briefly tried using a memory stick as a Dropbox folder. I moved my default folder back to my desktop when I saw that Dropbox does not recommend using a memory stick.  But now I have these weird extra phantom files.

[Robert S.]

The "._" files you see are MacOS X system files. The reason you see them is because you placed your Mac Dropbox folder on a volume which doesn't respect the hidden attribute of those files (i.e. FAT). They can be safely deleted.

[Art G.7]

Thank you!  I appreciate your help.

[Philipp Z.2]

Hi, I have the exact same problem. I'm using a Qnap NAS with cloud sync for my dropbox. when I save a file from my mac onto the NAS, duplicate files as described above appear. Even if I can safely delete them: how can I prevent the duplicate files to appear at the first place? Is it a problem of the NAS file system or an OS X problem? This is scaring me big time...! 

[Robert S.]

As I said above, "._" files are MacOS X system files. The reason you see them is because the Mac Dropbox folder has been placed on a disk volume formatted with a non-Mac filesystem which doesn't respect the hidden attribute of those files. You can delete them, but they'll be recreated by your Mac every time you access those files.

The effect would have been mitigated by ensuring the target volume was first formatted to the native MacOS filesystem. However, I would also note that Dropbox are pretty clear that they don't support removable drives or network volumes.

[Art G.7]

Philipp, why is this scaring you big time?  

[Philipp Z.2]

Thanks Robert -- I didn't know that network volumes weren't supported. Good to know. And Art -- these things scare me big time because 1) I don't want double the amount of space on my dropbox and b) no one is going to help me if I delete stuff and things get lost forever... but now that I know that network volumes are not supported, I will have to do it differently or cancel my business account. I'll keep testing a bit before I do that though because I really love dropbox.

[Philipp Z.2]

Robert, I am using a QNap NAS with the Cloud Drive Sync (Dropbox) App. So, what you are saying is that QNap does something unsupported by Dropbox? If that is so, I would just bring it right back to where I bought it from...