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Space Usage

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Applies to

  • Data ONTAP
  • Storage Efficiency

Answer

This article contains a list of most common questions regarding space usage and can be used to narrow your search to the more common questions and issues. However, it is not a comprehensive list.

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 in an aggregate allocated?

  • WAFL reserve WAFL reserves a 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 it cannot be changed.
  • Snapshot reserve percentage of disk space reserved for snapshots for each of the volumes in the system. Reserve space can be used only by snapshots and not by the active file system.

aggr_space_diagram.jpg

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.
  1. 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. The available disk space on a disk is rounded down as shown here.
  • How many spares are available in the system? Spare disks are not calculated in the total usable space.
Run the sysconfig –r command to determine the quantity.
  • Are you aware that there is a 10% reduction in the total usable space designated for WAFL overhead?
  • Is the system configured as a 'Flash Pool?
    This feature is first available in Data ONTAP 8.1.1. 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.

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