Here are some quotes from the Western Digital forum. I think it's unbelievable that WD hasn't hasn't issued a warning on their website yet. So customers keep loosing their data >>>
Help, my 6T raid (2 x 3T) external mac hard disk suddenly become no content in it?
I have just lost everything from my 6TB HD
Yesterday morning after starting my mac I found that all data is gone from My Book Studio II - the volume name has reverted to the default one, the drive is empty, WD RAID manager reports all healthy with 0% space used.
I also got this problem after installing Mavericks yesterday...this morning I almost got some heart faliure...
I Checked the WD with DiskDrill, and all the files are there and recoverable. (tested on a small amount, but no file structure....13 yrs of files in erratic order...oj oj. )
Same happened to me with mavericks (also RAID1), I had to reformat the drive.
Same thing happened to me with a WD My Book Studio Edition II 6TB. After calling WD numerous times they gave up and asked me to ask Apple what Mavericks does to their raid drive and to try recovering my data with a recovery software. 5TB archive gone at the moment, with a partial backup. I've never seen anything like this. Very serious and desperate situation.
As soon as I installed OS X 9.0 I received an error message that my WD External drive was not compatible, and since then all backups have failed.
My drive was killed too. Looked just like ccontreras' screen shot, with that EFI volume as well.
RAID 0, My Book Studio II 6 TB, connected via Apple's Thunderbolt-to-FireWire-800 adapter.
After the inital install of Mavericks everything was okay.
After restarting "Poof" Data gone. The WD Raid Manager kicked in and all was lost. Now there is one partition called EFI and one called MyBook.
I am in the same situation, cannot find any data on the My Book Studio, this is ridiculus.
Same to me. All data are gone after installing the Maverisks. I can read the content after installing Maverisks. But after I start my iMac tonite, all data are gone. But, the data in other WD external disk are still there. Only the one with raid 1 are gone.
And here are some quotes from the Apple forum >>>
I have experienced the same problem. I've lost 22 TB of data on multiple external drives (firewire, eSATA, USB) and some multiple times just as I rebuilding them. I disconnected a 6TB WD MyBook.
I just now lost an INTERNAL 4TB hard drive (replaced with an empty MyBook partition plus an EFI showing in sidebar of Finder) which has a Drobo NAS backup.
I have just another example of the update to OS X 10.9 causing hard drives to be displayed as empty.
Update completed on the MacBook Pro without problem but after restarting 4 hard drives where first renamed as 'EFI' and then renamed as 'mybook'.
1 drive was a WD MyBook connected via firewire. 2 where Samsung s2 portables, and 1 was a Seagate. These were connected via USB.
I have similar issues. I use two WD MyBook external drives which I created a raid 0 in Mountain Lion's disk utility. After Mavericks install I'm unable to mount the raid partition even though it is recognized in disk utility and the raid is "online".
as I've mentioned above I encountered the same problem, but with the combination Firewire MyBook Studio II + WD Software + USB Mybook + Mavericks. So it can't really be Firewire / Thunderbolt related for USB is also affected.
Totally agree with you. I've lost my 5 TB (backups, iTunes media, DVD, CD archive and 20 years of my software projects and even more resources, paid articles/books/libraries etc.) this morning. Everything was fine last night. Today, system erased everything without any warning!!!
I am also in the same situation, I'm desperate, I have 13 years of photos and videos LOST!
The second backup disk is a WD and therefore this has been canceled.