Skip to main content
NetApp Knowledge Base

How is space utilization managed in Data ONTAP SAN environment?

Last Updated:


Applies to

  • ONTAP 9
  • SAN
  • FlexPod


Layers of storage
  • Aggregate is a collection of physical disk space that is a container for one or more RAID groups
  • Within each aggregate, there is one or more FlexVol volumes
  • FlexVol volumes are allocated as a portion of available space with an aggregate. It contains one or more LUNs for use with iSCSI, FC or FCoE protocols
  • The file system at the aggregate level is maintained by ONTAP, and the FlexVol WAFL file system as well, but the LUN file system is maintained by the SAN client OS
    • This can create differences when looking at space at different layers

Example: A Windows client will view the NTFS file system formatted on a LUN, but ONTAP will only see the blob of data in the LUN and report LUN, volume, and aggregate space separately.

Space utilization managed in Data ONTAP SAN environment 

Storage efficiency features

See Storage Efficiency.

Volume space guarantee settings

See Space Guarantees

Space allocation in an aggregate
See the article Space Usage
Snapshot of a LUN

See the article How does a Snapshot of a LUN work?

Purpose of LUN space reservation
  • To allocate space equal to the size of LUN during LUN creation
  • To reserve space for overwrites (fractional reserve) once snapshots are taken to the size of LUN

See Understanding space reservations for LUNs

Manage Snapshot copy reserve

See Managing the Snapshot copy reserve

Running out of space

To view options if you are running out of space, see Space Usage

Additional Information

Reclaiming space

See the article How to reclaim space in an aggregate that is full


NetApp provides no representations or warranties regarding the accuracy or reliability or serviceability of any information or recommendations provided in this publication or with respect to any results that may be obtained by the use of the information or observance of any recommendations provided herein. The information in this document is distributed AS IS and the use of this information or the implementation of any recommendations or techniques herein is a customer's responsibility and depends on the customer's ability to evaluate and integrate them into the customer's operational environment. This document and the information contained herein may be used solely in connection with the NetApp products discussed in this document.