Understanding Storage Spaces capacity descriptions

Question

I have a Storage Spaces array in Windows 10 consisting of 7 SATA HDDs ranging from 3TB -> 8TB each (-edit- for completeness, those drive capacities are: {3, 4, 4, 4, 4, 8, 8}).

I'm trying to understand the Storage Spaces capacity values, shown below:

The section above the drive Name & Letter makes sense in isolation:

• 15 TB
  • defined size, with thin provisioning allowing it to exceed actual available capacity
• Using 14.6 TB pool capacity
  • the actual available configured capacity

And the 31.8 TB "Total pool capacity" makes complete sense as the sum of the actual disk capacity from each drive.

But...

1. Why is only 14.6 available?
   • I've defined my size as 15 TB
   • It says I have 17.2 TB available
2. What's the relationship here of the 22.5 TB "Including resiliency"?
3. What is my actual real max configurable usable capacity?
   • I expected to have around 20 TB (66% of 32) - so I'm guessing it's actually only 17.2, but then see question #1

Answer 1

You’re just confusing some numbers and meanings.

1. Why is only 14.6 available?

Nowhere does it say 14.6 TiB are available. It says 14.6 TiB of pool capacity are currently used for the Archive volume. That means you have ~9.7 TiB of data on this volume.

2. What's the relationship here of the 22.5 TB "Including resiliency"?

15 TiB data + 50% parity = 22.5 TiB

It’s like RAID 5. The 15 TiB is what you entered in the input box.

3. What is my actual real max configurable usable capacity?

Your math is correct. However, you are confusing the numbers. 31.8 TiB of total capacity - 14.6 TiB currently in use = 17.2 TiB currently unused.

With resiliency, you can use ²/₃ of the total capacity for user data—21.2 TiB.