A volume can be configured to grow and shrink automatically in response to space usage requirements. Automatic growing occurs when used space exceeds an autogrow threshold. Automatic shrinking occurs when used space drops below an autoshrink threshold.
The autosizing feature consists of two possible functionalities:
Automatic growth can provide additional space to a volume when it is about to run out of space, as long as there is space available in the associated aggregate. When the volume's free space percentage is below the specified threshold, it continues to grow by the specified increment until either the free space percentage arrives at the threshold or the associated aggregate runs out of space.
If a volume does not have enough space for a Snapshot copy to be created, an attempt to create a Snapshot copy does not cause the volume to automatically grow. In this case, the Snapshot copy creation fails.
The autoshrink functionality is only used in combination with autogrow to meet changing space demands and is not available alone. Automatic shrinking helps to more accurately size a volume and prevents a volume from being larger than it needs to be at any given point. The volume shrinks and returns space to the aggregate if the guarantee type is volume.
Because the size of the Snapshot reserve is a percentage of the size of the volume, Snapshot spill can start to occur or increase as a result of a volume shrinking.