Customer have a storage pool which has 800GB free space, but customer can only reduce 120G space when he tried to recycle space to disk domain.
In disk domain layer, the data unit is Chunk Group(CKG), but in storage pool, it’s Extent.
When customer create storage pool, the disk domain allocate CKGs to storage pool. But when customer create LUN, the storage pool allocate Extents to LUNs.
The default Chunk size is 64MB, and default Extent Size is 4MB. If you create storage pool in 8D+1P, the CKG size is very large. Far more larger than Extent.
After customer create/delete LUN, there will be many CKGs have free space but not totally free. So, storage pool can’t reduce them to disk domain.