At hardware level I have RAID 5 with 4 HDs configured as one disk array.
At OS level I have NW65 SP6 and 3 partitons:

I want to add + 2HDs, so I would have a disk array with 6 HDs. The extra space I want to allocate to the volume DATA.
What would be the best procedure to do so? I want to avoid going to tapes and restore from scratch.

Thank you in advance.