I have a 2012r2 storage server with 12x 6TB HDD. The drives shows up with 5.46 TB capacity which is expected. What is unexpected is creating the array in powershell. I would like to setup the 12 drives as a single dual parity space. Using the command
New-VirtualDisk -StoragePoolFriendlyName 72tb -FriendlyName HDD_Parity -UseMaximumSize -ResiliencySettingName Parity -ProvisioningType Fixed -PhysicalDiskRedundancy 2
I get a reported capacity of 48.88 TB. Using n-2 x 5.46 TB I should see 54.6 TB however 48.88 / 9 = 5.43 TB or roughly n-3. Specifying columns manually at 12 gives the same results, columns 11 drops the capacity by one more drive and so on.
If I switch routes and use
New-VirtualDisk -StoragePoolFriendlyName 72tb -FriendlyName HDD_Parity -UseMaximumSize -ResiliencySettingName Parity -ProvisioningType Fixed -PhysicalDiskRedundancy 1 -NumberOfColumns 6
which if I am not mistaken is 2x 6 drive single parity arrays striped or spanned? I get 54.57 TB which aligns with n-1 x 2 or 5.46 TB x 10.
So where is the missing drive with the dual parity virtual drive? It's not reported as a hot spare and I would rather not throw away the capacity of a third drive that isn't being used in any conceivable way.