You have an aggregate with 10 TB free. You create a 1 TB volume with space-guarantee set to none. In that volume, you create a 500 GB LUN with space-reserve enabled. How much space is available in the

10 TB would only be correct if neither the volume nor the LUN reserved any space, but the space-reserved LUN does consume 500 GB from the aggregate immediately upon creation.

When a volume has space-guarantee=none, the volume itself does not pre-allocate space from the aggregate, so the 1 TB volume creation does not reduce free space. However, a LUN with space-reserve enabled still claims its full 500 GB from the aggregate at creation time, reducing the 10 TB of free aggregate space to 9.5 TB before any data is written.

8.5 TB would imply 1.5 TB was consumed, which would only occur if the volume also held a full space guarantee (using 1 TB) in addition to the 500 GB LUN reservation.

9 TB would imply exactly 1 TB was reserved, which would be the result if the volume had space-guarantee=volume reserving 1 TB, not the none setting described in this question.