NAS vol1 will shrink in size when the volume is 40% full. This is because the volume autosize mode is set to grow_shrink, which means that the volume will automatically grow or shrink based on the space usage and the specified thresholds. The shrink threshold is set to 60%, which means that the volume will start shrinking when the space usage falls below 60%. However, the volume will not shrink immediately, but will wait for a period of time (by default, 24 hours) to avoid frequent resizing. The volume will shrink to the minimum size that is required to accommodate the current data plus 10% free space, or the minimum size specified by the user, whichever is larger1. In this case, the minimum size is not specified, so the volume will shrink to the size that has 10% free space. Therefore, the volume will shrink when the space usage is 40%,as that is the point where the volume has 10% free space after shrinking. References :- Configure volumes to automatically grow and shrink their size