Can anyone save my external hard drive?

Question

Hi all,
This is probably the first time ever that I have to ask a question myself. Usually when I have any problems I can find a solution in other people's solved threads. But not this time and I'm really frustrated. If any of you can help me with this I will be eternally grateful.
I have a 1TB WD external hard drive with 500Gb of millions of files, really important data that is not copied anywhere else right now.
Around the time I upgraded to Maverick's I think (not 100% sure) I started having problems when I wanted to copy files from the HDD. Some files would randomly give the error "The operation can’t be completed because the item X is in use". Some not, but since I have millions of files, I would try to copy folders, and whenever one of these files gave an error, the whole operation would be canceled and all the copied files deleted. Copying one by one is not an option, especially because there are some that don't even work individually, maybe 1/3 of them, I don't know.
I started looking on the internet about the problem and I found many people having the same one. However, they circumstances were usually different, not wanting to copy from an external HDD, but maybe they just wanted to delete some file or talking about some network thing saying some terms that I don't understand like NAS, SMB shares, AFP, so I thought that that wasn't my case. For the ones whose circumstances were similar, I tried every single option that I found. Here is what I tried so far:
-Copying not the files but the "mother/s folder/s (in many different ways and it definitely didn't solve anything).
-Killing some process called "Unmount blabla" I don't remember.
-Disabling the icon preview in finder. I thought it would solve it because everyone said it did, but not for me : (
Note that so far, while I couldn't copy the files, the speed at which it tried or it copied some was a normal one.
Then I went to disk utility and tried to repair the disk, thinking something was wrong with it. The first time I could verify, but not repair. It didn't solve anything obviously. The second time I couldn't even verify it.
Then I decided to upgrade to Yosemite thinking this might solve a possible Maverick's problem.
My God, it didn't. Now, not only it keeps saying that the files are in use. Now every time I plug the HDD, it takes around 15 minutes without recognising it, until finally a message pops up "This disk can't be repaired. You can still copy files from it, but backup as many as you can and then erase the volume". (It seems it automatically tries to repair it now?)
As if that wasn't enough, once the device is recognised. It seems that the speed at which it reads the files inside has been dramatically decreased. If I try now to copy some files. Like an iPhoto Library of 4 Gb, it copies at approximately 0,05 Mb per second, with an estimated time of 24 hours for 4 mere Gb. It would take a whole year to transfer 500Gb. But of course, not even that since after waiting one hour, it gives the same problem "file in use".
It seems to be more the reading than the writing since when I copy big files that are not in populated folders (and that are not the "evil / in use" files) it does it faster.
Erasing is not an option, there are just too many important things. I know, I should have had 2 copies, but this is the situation now...
I tried downloading a recovery software and I tried with some Stellar Phoenix Data Recovery or something like that. The first times I tried recovering files from it, it would do it at the same ultra slow speed. One of the times, randomly it copied all the files at a normal USB 3.0 speed (I had forgotten how fast that was), but all the files were completely unreadable. When I tried to open them it said they were damaged.
However, it's not that the files are damaged because when I try to copy them manually they can be opened normally. But of course, at the slowest speed in the world and only a fraction of them.
If you can help me solve this issue, I really would be in debt forever. I haven't end up in a dead end like now and I really need to recover the data.
Thank you so much in advance.
Jose

Answer 1

The device may be formatted for Windows, as NTFS. The format is readable, but not natively writable on a Mac. To write to the device, you must either reformat it (erasing all the contents) or install third-party software to enable write access to NTFS.