Suppose I that I may have multiple RAID groups on my system. However, one of my aggregate has 1RG with the disk details as mentioned and need some more space on it. On my disk chassis, I only have two unpopulated bays to populate disks. So, in such cases how could we proceed cos for creating a new RG DP, we need atleast 3 drives. OR Is it possible to remove drives from the existing RG and use that drive for the creation of the new RG ?
You can't remove disks from a RG or Aggr - you would need to destroy it / re-create it (this would destroy all data in the aggregate unless you move it first).
If adding disks to an aggregate will start a new raid group of type DP, you would need to add 3 disks. And if you could do that, you would only effectively get the capacity of 1 disk added to the aggregate. If the RG size is really large, you should try to add many disks to it to get useful capacity.