If you install OS X 10.9 the problems starting. To fix the problems I returned to the backup and restored OS X 10.8.5 After restarting with sofware 10.8.5 the Pegasus Promise R4 Raid5 disk was empty and the name from the disk was changed to MyBook? By By all data. The disk is working normal but data is gone. The problem is possible coming from the program WD drive manager. The drive is full formatted and renamed to MyBook. (for this I think it is the drive manager from WD) I have open a case to Promise, till now reaction was "Response By:- Thomas Paraschos 24th October 2013 at 4:53 Hello, we don`t know anything about this problem. But we will try to reproduce the "Error". Please let us know was the Pegasus always connected during the update to your MAC ? The Promise Pegasus R4 disk is connected with thunderbolt connector and from there the cable is join over to FireWare 800 and 3 disks are connected 2x my book studio editionII and 1x wd my passport studio with the WD disks no problems. I have brought the disk to a company to recover all the software. The explain "The device has been formatted, and has a few other software/logical problems." Next week I know what is possible to recover, according to this company possible 100% recovery.