Cannot setup RAID with Disk Utility using 3TB drives (1TB Drives work)

I have a pair of 3TB drives that I'm trying to setup in a RAID1 config using disk utility. It fails every time with a fairly non specific error and when I verify either disk it reports an issue with the EFI partition.

If I then fix the disk, it reports the disk as fixed, but then verify shows the same error...

I then tried it with two other smaller disks and it worked first time. Is there an issue with OSX and 3TB drives that allows them to be used for data, but not for RAID?

Andrew