if you can help it, try to always expand SAS tier in 5 drive increments. So can you expand the pool by 5 drives and then use LUN Migrator to migrate LUNs from other raid groups to storage pool LUNs. Once the other raid groups are free ..add the remaining 15 drives to the pool.
when we got the VNX 5300 SAN in 2013 it was setup by an EMC tech and for some reason he set it up using Raid Groups.  When we purchased a new additional shelf we were told to configure it using Storage Pools.  I’m just trying to figure out best practice for moving our SAN from Raid Groups to Storage Pools.  I have an empty Raid Group that I would like to delete and expand our Storage Pool with.  Is this ok or would it be better to create a new Storage Pool?  Anything to look out for?  Thanks!
Want to Remove Raid Group and Expand Storage Pool