Hello,
By design Pool B cannot 'borrow' space from Pool A or visa versa.
How you wish to carve up the space on the D2700 will really depend on your needs. You should think about how each Pool will need to grow. For example, a database on Pool A may be for storing inventory, while the database on Pool B may be for transactions. As your business grows, you may need to increase your inventory by 10% which will lead to a transaction increase (hopefully) of 25%. This means both pools will need additional disk groups but you will need more allocated space on Pool B. Using this example I would then create a new disk-group for Pool A (10 drives) that is smaller than the disk-group created for Pool B (14 drives) + 1 global spare. For RAID6 stay within the Power of 2 - number of data drives (nonparity) contained in a disk group should be a power of 2.
To provide some best practices I do suggest you leave some disks available and assign them as global spares. To provide better redundancy I would create all disk-groups as RAID6. Be sure you have both background scrub and disk scrub enabled as well as alerts set to a WARNING level.
Good luck!
Cheers,
Shawn
I work for Hewlett Packard Enterprise. The comments in this post are my own and do not represent an official reply from HPE. No warranty or guarantees of any kind are expressed in my reply.