Partition Tab not showing in Disk Utility

Hello again everyone,

I'm attempting to partition my LaCie 2TB (RAID1) Disk in Disk Utility, however the partition tab is not showing up..

There are 4 items visible in the Disk Utility window:

1) the Internal OS Disk

2) the LaCie 2TB (RAID1) Disk

3) & 4) the two slices/partitions of the LaCie mirrored RAID

I select the 2TB LaCie RAID1 Disk, however it only shows the "First Aid" & "RAID" tabs.

The "Partition" (as well as "Erase" & "Restore") tabs are not available or shown.

When I select the Internal OS Disk all the Tabs are shown, and when the 2 slices or partitions of the RAID1 are selected it shows the "First Aid, Erase, Partition, Restore" tabs..

Am I missing a step here?? I know I'm not supposed to select the slices/partitions of the RAID, but instead to select the LaCie 2TB Disk itself, however this is the only option which does not show any "Partition" Tab..

Any assistance is GREATLY APPRECIATED.. Thank you!