I used the HP Smart Storage Administrator to add my 3 new 8TB disks and extend the array. The logical drive shows that the space has been added, but in Disk Management the space is not allocated. When I go to extend the disk I get the messsage "The volume cannot be extended because the number of clusters will exceed the macimum number of clusters supported by the file system.". There for I have around 20TB of space that I cannot added to the Logical Drive.
<UPDATE>
So it appears it's a limitation to the cluster size. The current cluster size is set to 16K which will only allow 64TB partitions. I've allocated as much as I could to the existing partition, leaving about 1.4TB unallocated.