I am running OS X 10.10 on a Mac Pro and I am connecting a 2TB My Book VelociRaptor Duo to it via Thunderbolt. If I leave the drive formatted in RAID everything works just fine. I need it formatted in JBOD, but whenever I do so, the drive mounts for about 3 seconds and automatically ejects itself. After it ejects I can see it in Disk Utility, where I can right click and mount it again, but it still only stays mounted for about 3 seconds. Can anyone help? I can't even use this drive because of this.
I have the exact same problem with a WD My Passport Pro 4 TB.
When formatted in Raid 0, it mounts as a 4 TB disk and stays mounted as expected.
When JBOD'd as two 2 TB disks, they mount, and then unmount 3 seconds later, remount and re-unmount until they stop mounting. Disk Utility sees both disks and will remount them, but won't mount them durably.
Interesting remark : this happens in Yosemite 10.10.5. In Mavericks 10.9 AND, astonishingly, in El Capitan 10.11 beta 7, my My Passport Pro JBOD'd twin disks mount and work absolutely as one would normally expect !