Free space for NSS volumes is currently calculated as volume free space + purgeable space.
Used space for NSS volumes is currently calculated as total size – calculated free space. This means that the volume compressed size is included along with actual space used.
For NSS volumes that are oversubscribed on a shared NSS Pool, the volume total size of each volume in the pool will change as data is added or removed from other volumes in the pool. This is known behavior for oversubscribed volumes.
Oversubscribed NSS volumes are defined as two or more NSS volumes that are set to grow to the size of a shared NSS Pool.