4TB disks on ReadyNas Ultra 6?

aussieboxer wrote:
IF one of the ULTRA dies (say in 5 years time but hey I have some servers running VMs at home over double that age) - can I take all the disks out of the other live one one - plug in the disks for the dead ultra 6 (presumably in exactly the same BAY) and it will read it (so I can copy to a new NAS ?)

Assuming the problem is with the chassis not the disks, yes.

aussieboxer wrote:
I run linux Ubuntu but I assume to access them through a PC I would need to a) plug ALL 6 HDD into the PC and b) define the volume (?) to linux before if could access the data I couldn't access them disk by disk I assume Thanks and sorry to be slow....

You would have to enter some commands in the Terminal to assemble the RAID, scan for volumes, activate them, mount them etc. If your system doesn't have the required packages you could download them using apt-get.