Gabor.....
Dan_WGBU, our favorite HP engineer, has weighed in on this. There are two issues...... one is driver related and the second is that the boot drive cannot be a 3TB one. Here are two posts to review, and this is true for the Z400, Z600 and Z800:
The take home from Dan is that 3TB drives can be used as a single partition if they are a non-boot documents drive (which is how most of us should be using them.... with a SSD as our boot/applications drive).
The other post has to do with what storage controller driver one might be choosing to use.
I have a 3TB drive handy..... I'll plug it into this Z600 and get back to you in a few minutes about how it is formatted and how it worked, plus my storage driver being used.
Scott