Considerations when using thin provisioning with Infinite Volumes

You can use thin provisioning with an Infinite Volume, enabling you to allocate more storage to users than is physically available. Before using thin provisioning, you should understand what it is, where and when it is configured, and what its advantages and disadvantages are.

What thin provisioning is

With thin provisioning, the size of an Infinite Volume is not limited by the size of its associated aggregates. You can create a large volume on a small amount of storage, adding disks only as they are required. For example, you can create a 10 TB volume using aggregates that only have 5 TB of available space. The storage provided by the aggregates is used only as data is written. Thin provisioning is also called aggregate overcommitment.

The alternative of thin provisioning is thick provisioning, which allocates physical space immediately, regardless of whether that space is used for data yet. The allocated space cannot be used by any other volumes. When you use thick provisioning, all of the space required for the volume is allocated from the aggregate at the time of creating the volume.

Thin provisioning affects only the data constituents of an Infinite Volume. The namespace constituent and namespace mirror constituents of an Infinite Volume always use thick provisioning. For example, if you create a new Infinite Volume with a 2 TB namespace constituent and use thin provisioning, the namespace constituent will consume 2 TB of space even if the Infinite Volume does not contain any data.

When and where thin provisioning is configured

The way that you configure thin provisioning on an Infinite Volume depends on whether the Infinite Volume uses storage classes.

For an Infinite Volume without storage classes, thick and thin provisioning are configured at the volume level in the following way:

•	If you want to use thin provisioning, you typically specify it when you first create the Infinite Volume.

By default, an Infinite Volume created through the command line uses thick provisioning.

•	You can switch between thick and thin provisioning after the Infinite Volume is created.

If you change the setting later, you cannot change the Infinite Volume's size at the same time; you must change the size and guarantee of an Infinite Volume in separate operations.

Before changing a volume from thin provisioning to thick provisioning, you must ensure that the physical storage can support the provisioned size.

For an Infinite Volume with storage classes, thick and thin provisioning are configured at the storage-class level in the following way:

•	You can choose to use thick or thin provisioning for each storage class independent of other storage classes.

For example, one storage class of an Infinite Volume can use thin provisioning while another storage class of the same Infinite Volume uses thick provisioning.

•	All configuration of thick and thin provisioning is performed by using OnCommand Workflow Automation.

•	If an Infinite Volume uses storage classes, it is not possible to configure thick or thin provisioning at the Infinite Volume level.

Advantages of thin provisioning

Using thin provisioning with Infinite Volumes provides the following advantages:

•	Defers physical storage costs until the storage is actually required

Users receive the space allocation that they expect, and valuable resources do not remain unused.

•	Facilitates monitoring of aggregate usage

When you use thin provisioning, information about aggregate usage—for example, the Used Size, Used Percentage, and Available Size—reflects the actual space used to store data. When you use thick provisioning, aggregate usage information reflects the allocated space, which typically differs from the space that is actually used to store data.

•	In some cases, eliminates the need to change the volume size after adding disks

If you add more disks to existing aggregates, you do not have to resize the Infinite Volume to make use of the added capacity as long as the total size of the Infinite Volume's associated aggregates is less than the Infinite Volume's size.

Disadvantages of thin provisioning

Thin provisioning includes the following disadvantages:

•	If you have overcommitted your aggregate, you must monitor your available space and add storage to the aggregate as needed to avoid write errors due to insufficient space.

•	In a multi-tenancy environment, if you share aggregates among volumes that use thin provisioning, be aware that one tenant's aggregate space availability can be adversely affected by the growth of another tenant's volumes.

•	The process of balancing incoming files across data constituents is less effective when an Infinite Volume uses thin provisioning because the reported percentage of used space does not always represent the physical used space.

More information about thin provisioning

For more information about thin provisioning, see Thin Provisioning Deployment and Implementation Guide (TR-3965).