What is volume autosize in Data ONTAP?

What does volume autosize do?

• Volume autosize is a policy-based space-management feature in Data ONTAP that allows the volume to grow by an increment if the volume is nearly full.
• The nearly full threshold is defined by the flag wafl_reclaim_threshold.
• When a write is sent to the node that is larger than available space, Data ONTAP will try to write as much as possible before failing the write with a volume full message. 
  • During the next check, the volume will grow by increments until it has reached the minimum free space threshold. 
  • This means that autosize is best described as 'grow on use,' rather than 'grow on demand,' a distinction that should be remembered when planning thresholds and grow increments.
• Note that volume autosize does not infinitely grow the volume. 
  • The volume will grow until it reaches the maximum autosize value and then no more space will be allocated.

The syntax for enabling volume autosize is as follows:

Clustered Data ONTAP/ONTAP 9:

::> volume modify -vserver <vserver_name> -volume <volume_name> -autosize
-autosize-increment                -autosize-increment-percent
-autosize-grow-threshold-percent   -autosize-shrink-threshold-percent
-autosize-mode                     -autosize
-autosize-reset                    -antivirus-on-access-policy

Note: Starting in ONTAP 9, -autosize-increment is unavailable, as this value is dynamically determined by ONTAP.

For more details on above parameters refer to the documentation for the `volume modify` command

Data ONTAP 7:

> vol autosize  [-m [k|m|g|t]]
               [-i [k|m|g|t]] 
              [ on | off | reset ]
-m option sets the maximum size a volume is permitted to grow. Default setting is 120% of volume size at the time of creation
-i option defines the increment by which a volume is grown every time the volume is full. Default setting is 5% of volume size at the time of creation
on enables the feature
off disables the feature
reset resets the settings to default value.

Choosing reclaim policies:

In order to reclaim space which is determined by defining policies, with the use of the try_first volume option. The try_first volume option determines whether:

• Snapshot autodelete would be attempted first.
• Or volume autosize would be attempted first.

The possible try_first values are:

• snap_delete
• volume_grow