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How you can determine and control a volume's space usage in the aggregate

You can determine which FlexVol volumes and Infinite Volume constituents are using the most space in the aggregate and specifically which features within the volume. The volume show-footprint command provides information about a volume's footprint, or its space usage within the containing aggregate.

The volume show-footprint command shows details about the space usage of each volume in an aggregate, including offline volumes. This command does not directly correspond to the output of the df command, but instead bridges the gap between the output of the volume show-space and aggregate show-space commands. All percentages are calculated as a percent of aggregate size.

Only non-zero values are displayed in the command output. However, you can use the -instance parameter to display all possible feature rows regardless of whether they are enabled and using any space. A value of - indicates that there is no data available to display.

Infinite Volume constituents appear in the output of space usage commands as if the constituents were FlexVol volumes.

The following example shows the volume show-footprint command output for a volume called testvol:

cluster1::> volume show-footprint testvol

      Vserver : thevs
      Volume  : testvol

      Feature                                   Used    Used%
      --------------------------------    ----------    -----
      Volume Data Footprint                  120.6MB       4%
      Volume Guarantee                        1.88GB      71%
      Flexible Volume Metadata               11.38MB       0%
      Delayed Frees                           1.36MB       0%
      Total Footprint                         2.01GB      76%

The following table explains some of the key rows of the output of the volume show-footprint command and what you can do to try to decrease space usage by that feature:

Row/feature name Description/contents of row Some ways to decrease
Volume Data Footprint The total amount of space used in the containing aggregate by a volume's data in the active file system and the space used by the volume's Snapshot copies. This row does not include reserved space, so if volumes have reserved files, the volume's total used space in the volume show-space command output can exceed the value in this row.
  • Deleting data from the volume.
  • Deleting Snapshot copies from the volume.
Volume Guarantee The amount of space reserved by the volume in the aggregate for future writes. The amount of space reserved depends on the guarantee type of the volume. Changing the type of guarantee for the volume to none. This row will go to 0.

If you configure your volumes with a volume guarantee of none, you should refer to Technical Report 3965 or 3483 for information about how a volume guarantee of none can affect storage availability.

Flexible Volume Metadata The total amount of space used in the aggregate by the volume's metadata files. No direct method to control.
Delayed Frees Blocks that Data ONTAP used for performance and cannot be immediately freed.

When Data ONTAP frees blocks in a FlexVol volume, this space is not always immediately shown as free in the aggregate because operations to free the space in the aggregate are batched for increased performance. Blocks that are declared free in the FlexVol volume but that are not yet free in the aggregate are called "delayed free blocks" until the associated delayed free blocks are processed.

For SnapMirror destinations, this row has a value of 0 and is not displayed.

No direct method to control.
File Operation Metadata The total amount of space reserved for file operation metadata.

After space is used for file operation metadata, it is not returned as free space to the aggregate, but it is reused by subsequent file operations.

No direct method to control.
Total Footprint The total amount of space that the volume uses in the aggregate. It is the sum of all of the rows. Any of the methods used to decrease space used by a volume.