In some cases, enabling a feature in ONTAP might consume more space than you expected. ONTAP helps you determine how space is being consumed by providing three perspectives from which to view space: the volume, a volume’s footprint within the aggregate, and the aggregate.

View space allocation

A volume can run out of space due to space consumption or insufficient space within the volume, aggregate, or a combination of both. By seeing a feature-oriented breakdown of space usage from different perspectives, you can assess which features you might want to adjust or turn off, or whether you should take other action (such as increasing the size of the aggregate or volume).

You can view space usage details from any of these perspectives:

The volume’s space usage

This perspective provides details about space usage within the volume, including usage by Snapshot copies.

Use the volume show-space command to see a volume’s space usage.

Beginning with ONTAP 9.14.1, on volumes with temperature-sensitive storage efficiency (TSSE) enabled, the amount of space used on the volume reported by the volume show-space -physical used command includes the space savings realized as a result of TSSE.
The volume’s footprint within the aggregate

This perspective provides details about the amount of space each volume is using in the containing aggregate, including the volume’s metadata.

Use the volume show-footprint command to see a volume’s footprint with the aggregate.
The aggregate’s space usage

This perspective includes totals of the volume footprints of all volumes contained in the aggregate, space reserved for aggregate Snapshot copies, and other aggregate metadata.

WAFL reserves 10% of the total disk space for aggregate level metadata and performance. The space used for maintaining the volumes in the aggregate comes out of the WAFL reserve and cannot be changed.

Beginning with ONTAP 9.12.1, the WAFL reserve for aggregates greater than 30TB is reduced from 10% to 5% for ETERNUS AX series. Beginning in ONTAP 9.14.1, this same reduction applies to aggregates on all ETERNUS HX series, resulting in 5% more usable space in the aggregates.

Use the storage aggregate show-space command to see the aggregate’s space usage.

Certain features, such as tape backup and deduplication, use space for metadata both from the volume and directly from the aggregate. These features show different space usage between the volume and volume footprint perspectives.

Volume metadata and data metric reporting

Related Information

Historically, several of the volume space metrics have reported the total data consumed as a combination of two metrics: metadata and user data. Beginning with ONTAP 9.15.1, the metadata and user data metrics are reported separately. Two new metadata counters have been introduced to support this:

total-metadata

This counter provides the total metadata size inside the volume. It does not include the aggregate resident volume metadata. Reporting it separately helps to determine the logical data allocated by the user.
total-metadata-footprint

This counter is the sum of volume resident metadata and aggregate resident volume metadata. It provides the total metadata footprint of the volume inside the aggregate. Reporting it separately helps to determine the physical data allocated by the user.

In addition, several existing counters have been updated to remove the metadata component and present only the user data:

User data
Volume data footprint

These changes provide a more accurate view of the data consumed by the user. This has several benefits, including the ability to make more precise chargeback decisions.

ONTAP 9 Manuals ( CA08871-402 )

Determine space usage in a volume or aggregate

View space allocation

Volume metadata and data metric reporting

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