Understanding storage units

Storage units for managing disk space

You use the following storage units to configure and manage disk space on the storage system:

Aggregates
Traditional or flexible volumes
Qtrees
Files
LUNs

The aggregate is the physical layer of storage that consists of the disks within the Redundant Array of Independent Disks (RAID) groups and the plexes that contain the RAID groups.

A plex is a collection of one or more RAID groups that together provide the storage for one or more Write Anywhere File Layout (WAFL) file system volumes. Data ONTAP uses plexes as the unit of RAID-level mirroring when the SyncMirror® software is enabled.

An aggregate is a collection of one or two plexes, depending on whether you want to take advantage of RAID-level mirroring. If the aggregate is unmirrored, it contains a single plex. Aggregates provide the underlying physical storage for traditional and FlexVol volumes.

A traditional volume is directly tied to the underlying aggregate and its properties. When you create a traditional volume, Data ONTAP creates the underlying aggregate based on the properties you assign with the vol create command, such as the disks assigned to the RAID group and RAID-level protection.

Once you set up the underlying aggregate, you can create, clone, or resize FlexVol volumes without regard to the underlying physical storage.You do not have to manipulate the aggregate frequently.

You use either traditional or FlexVol volumes to organize and manage system and user data. A volume can hold qtrees and LUNs. A qtree is a subdirectory of the root directory of a volume. You can use qtrees to subdivide a volume in order to group LUNs.

For detailed information

For detailed information about storage units, including aggregates, and traditional and FlexVol volumes, see the Data ONTAP Storage Management Guide.

Where LUNs reside

You create LUNs in the root of a volume (traditional or flexible) or in the root of a qtree, with the exception of the root volume. Do not create LUNs in the root volume because it is used by Data ONTAP for system administration. The default root volume is /vol/vol0.