Thanks Greg 
This is my first Samsung disk so we'll see how it goes. On the mirror side of things, I have duplication switched on for all of my shared folders so this means there are automatically two copies on the server and these are always on different HD's. This is part of the reason I went with Samsung this time, so I have a different manufacturer. To my network I can't see the drive I've just added, all I see is the increase in available volume on the share. It's kinda a Raid 1 but implemented at the OS level. The neat thing about the Drive Pool is I can add any type of disk and the mirrored data is not encrypted in any way. I can remove one of the drives and place it into another machine and see all of the files as they are just on a standard NTFS partition.
That's pretty much how Linux software raid1 works too. i.e. I can take half the mirror and plonk it in another linux machine and read it, but as an added bonus, I can reconstruct the raid in another machine with a spare disk, using that half of the mirror.