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Storage window : Storage units for managing disk space

Storage units for managing disk space
To properly provision storage, it is important to define and distinguish between the different units of storage.
The following list defines the various storage units:
Plexes
A collection of one or more Redundant Array of Independent Disks (RAID) groups that together provide the storage for one or more Write Anywhere File Layout (WAFL) file system aggregates or traditional volumes.
Data ONTAP uses plexes as the unit of RAID-level mirroring when the SyncMirror software is enabled.
Aggregates
The physical layer of storage that consists of the disks within the RAID groups and the plexes that contain the RAID groups.
It 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.
Traditional or flexible 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.
A FlexVol volume is a volume that is loosely coupled to its containing aggregate. A FlexVol volume can share its containing aggregate with other FlexVol volumes. Thus, a single aggregate can be the shared source of all the storage used by all the FlexVol volumes contained by that aggregate.
You can use either traditional or FlexVol volumes to organize and manage system and user data. A volume can hold qtrees and LUNs.
After 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.
Qtrees
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.
LUNs
A logical unit of storage that represents all or part of an underlying physical disk.
You can create LUNs in the root of a volume (traditional or flexible) or in the root of a qtree.
Note: You should not create LUNs in the root volume because it is used by Data ONTAP for system administration. The default root volume is /vol/vol0.
For detailed information about storage units, see the Data ONTAP 7-ModeStorage Management Guide.
Parent Topic: Storage window


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