I can't get Storage Spaces on Windows 8.1 to extend past 15.8tb

I recently purchased some additional HDDs for my storage machine.  I have had 15.2tb allocated to my storage pool for while, and purchased a couple more drives to extend up to 20.9tb.  When I go to "Control Panel\System and Security\Storage Spaces\Change a storage space" I can see Total pool capacity 20.9 TB, and Available pool capacity: 5.01 TB.  When I changed the selection for Storage space size (maximum): to anything above 15.9 TB, the message "The specified size is not valid" and the "Change storage spaces" button is grayed out.

I have seen some postings about the volume is set to 4 KB.  I don't know what this means or if it has an affect on my situation.

Can anyone lend a guiding hand to how I can extend this past the 16TB range?

Thanks

Hi,

According to your description, I think it is related to NTFS cluster size.

Using the default cluster size of 4 kB, the maximum NTFS volume size is 16 TB minus 4 kB.

With Windows 8, the maximum NTFS file size is 256 TB minus 64 KB

I suggest you change the cluster size to 64KB.

Regards,