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3.3.5. Thinly-Provisioned Logical Volumes (Thin Volumes)
As of the Red Hat Enterprise Linux 6.4 release, logical volumes can be thinly provisioned. This allows you to create logical volumes that are larger than the available extents. Using thin provisioning, you can manage a storage pool of free space, known as a thin pool, which can be allocated to an arbitrary number of devices when needed by applications. You can then create devices that can be bound to the thin pool for later allocation when an application actually writes to the logical volume. The thin pool can be expanded dynamically when needed for cost-effective allocation of storage space.
Thin volumes are not supported across the nodes in a cluster. The thin pool and all its thin volumes must be exclusively activated on only one cluster node.
By using thin provisioning, a storage administrator can over-commit the physical storage, often avoiding the need to purchase additional storage. For example, if ten users each request a 100GB file system for their application, the storage administrator can create what appears to be a 100GB file system for each user but which is backed by less actual storage that is used only when needed. When using thin provisioning, it is important that the storage administrator monitor the storage pool and add more capacity if it starts to become full.
To make sure that all available space can be used, LVM supports data discard. This allows for re-use of the space that was formerly used by a discarded file or other block range.
For information on creating thin volumes, see Section 5.4.4, “Creating Thinly-Provisioned Logical Volumes”.
Thin volumes provide support for a new implementation of copy-on-write (COW) snapshot logical volumes, which allow many virtual devices to share the same data in the thin pool. For information on thin snapshot volumes, see Section 3.3.7, “Thinly-Provisioned Snapshot Volumes”.