I had foreseen such trouble, so when I received a fresh R6 x 1TB, I decided to experiment a bit. I deleted the factory installed 6-disk RAID5, had a 4-disk RAID5, a single global spare and a single disk partitioned and formatted by the Pegasus Utility as 500 MB. When extending the 500 MB to 1 TB, using the Promise utility, the utility says the logical drive has 1TB capacity.
As you indicate, Disk Utility cannot expand to the full 1TB logical drive size.
So part of the answer is 'it is independent of RAID configuration'.
To save other people the trouble of testing, I decided to consider my options.
To test if it has to do with the formatting by Pegasus Utility, I deleted the logical drive and made a new logical 500GB drive, this time with the 'format' option OFF. I then partitioned the 500 GB logical drive using Disk Utility and set it to 500 GB. In the Promise utility, I started the Background Activities Migration option and expanded the RAID0 500 GB volume to 1000GB.
diskutil list
shows
Unfortunately, Disk Utility still fails to extend the current partition layout from 500 GB to 1 TB. Restarting the subsystem/MacOS did not help.
Re-partitioning the logical volume in Disk Utility (and thus wiping all data on the partition) DOES work however. So it is "just" MacOS/Disk Utility not being able to expand the already present partition.
I notice that if you create another logical drive on the remaining space of the disk, it appears as a new partition on a new disk in Disk Utility(screenshot above then shows
/dev/disk3/
), not as a second partition on the same disk (as would have been the case on an internal disk or USB/FireWire external single disk). This even happens when you create both partitions on the same disk array at the same time.
Using diskutil I found out that even though Pegasus Utility and Disk Utility both report disk capacity to be 1 TB,
diskutil resizeVolume disk2s2 limits
shows
Current size: 499.7 GB (499656028160 Bytes)
Minimum size: 5.8 GB (5816856576 Bytes)
Maximum size: 499.7 GB (499656028160 Bytes)
The only way one can use the maximum capacity of new disks, seems to remove disk 6 from a 6-disk RAID5 (net capacity 5 TB), copy 1 TB to the now externally attached 1TB disk, swap disk 6 (auto rebuild off) with a 4 TB disk, copy all data to the 4TB disk, swap the remaining 5 disk with 4TB disks, make them RAID0, copy from disk 6 to RAID and then upgrade from RAID0 to RAID5 by adding disk 6 to the RAID. This adds redundancy but does not change the maximum disk size, hence does not require resizing the partition.
Finally copy the 1TB disk content back to the now 20 TB RAID5.
