ONTAP Space Usage

Overview

Space usage spans from the physical disk layer to the logical file system, starting with carving out an aggregate on the disks and creating a volume on the aggregate where files and LUNs reside.

How is the space allocated in an aggregate?

• WAFL reserve WAFL reserves a 10% of the total disk space for aggregate level metadata and performance (5% in ONTAP 9.12.1 and higher.) The space used for maintaining the volumes in the aggregate comes out of the WAFL reserve and it cannot be changed.
• The Snapshot copy reserve sets aside a percentage of disk space for Snapshot copies, 5% by default. When the Snapshot copy reserve is exhausted, Snapshot's use space in active file system.

Documentation:

• How to determine space usage in a volume or aggregate
• Usable and physical disk capacity by disk size

Clustered Data ONTAP:

How to determine space usage in a volume or aggregate

ONTAP 9:

• How to determine space usage in a volume or aggregate
• Monitoring the space utilization for FabricPool
• Difference in space usage displayed by a quota report and a UNIX client
• What the volume footprint is

Common issues:

The specific failure symptom can vary depending on your configuration and version of Data ONTAP.

1. Aggregate is nearly full and needs additional space.

Resolution:

The following options are available to increase the available space in an aggregate:

• Add disks to the aggregate.
• Move some volumes to another aggregate with available space.
• Shrink the size of volume-guaranteed volumes in the aggregate.
• You can do this manually or with the autoshrink option of the autosize capability.
• Change volume guarantee types to none on volumes that are using large amounts of space (large volume-guaranteed volumes with large reserved files) so that the volumes take up less space in the aggregate.
• A volume with a guarantee type of none has a smaller footprint in the aggregate than a volume with a guarantee type of volume.
• Delete unneeded volume Snapshot copies if the volume's guarantee type is none.
• Delete unneeded volumes.
• Enable space-saving features, such as deduplication or compression.
• (Temporarily) disable features that are using a large amount of metadata.

Note: If you have Snapmirrors running , they may be preventing you from reclaiming space on the aggregate. stop the Snapmirrors while you work on creating additional space.

2. Where did my space go? Not seeing the expected amount of space.

Resolution:

• Are you aware that the disks are right sized?
  When you add a new disk, Data ONTAP reduces the amount of space on that disk that is available for the user data, by rounding down. This maintains compatibility across disks from various manufacturers. The available disk space listed by informational commands such as nodeshell's 'sysconfig -r' output is less for each disk than its rated capacity; however, this is normal. 

• How many spares are available in the system? Spare disks are not calculated in the total usable space.

• Are you aware that there is a default 5%-10% reduction in the total usable space designated for WAFL overhead?  Beginning in ONTAP 9.12.1, the WAFL reserve for aggregates greater than 30TB is reduced from 10% to 5% for AFF platforms and for the FAS500f platforms. Beginning in ONTAP 9.14.1, this same reduction applies to aggregates on all FAS platforms, resulting in 5% more usable space in the aggregates.

• Is the system configured as a 'Flash Pool?
  If an aggregate is configured as a 'Flash Pool', you will see the hybrid_enabled option set to on in aggr options. You will also see the hybrid_enabled flag listed in aggr status.
  
  If the aggregate is hybrid enabled, then the disks SSD RAID Group, as identified in aggr status -r or sysconfig -r, will not increase the usable space in the aggregate. These disks are used for cache only.