DL380 G10 - P816 controller - Extending LD produces error about max size, even though there is more space in the Array

I believe the reason I couldn't allocate all of the 619995 MB is that some of that storage is needed for the RAID 5 parity. I expanded LD 1 to the max allowed and it was allocated 551104 MB as per the amount that SSA told me could be allocated to it, despite showing 619995 MB of unused storage.

Note that 551104/619995 equals 8/9. Note also that I have 9 drives in a RAID 5 configuration so that is essentially 8 drives of data and one drive for parity.

Hence when SSA reports "Unused Space" that space includes space needed for parity so you won't be able to use all of it for your data.

Also, that means that unused space in the array is available to any LD in the array, which is what you would expect from HP's documentation. Just don't forget to deduct for parity.