Traditionally, when a system allocates storage for a logical volume, the allocation is dedicated to that volume. This dedication prevents other volumes from accessing this storage, even when the amount that is allocated is never used by the owning volume.
Thin provisioning allows you to leverage this unused storage. To leverage unused storage, perform the following actions:
- Allocate capacity based on future needs.
- Draw from a common pool of storage as the allocated capacity is consumed.
Thin provisioning on an Oracle FS System allows you to create a logical volume of any size without committing the requested capacity at the time that you create the volume. Each volume appears to have all of the storage that the volume needs for ongoing operations. The difference is that the physical capacity is not actually locked to a particular volume.
All logical volumes in an
Oracle FS System have two properties that are related to the logical capacity of the volumes. Also, whether a logical volume is thinly provisioned depends on the relationship between the initial values of those two capacities.
- Capacity
- Addressable logical capacity
The maximum amount of storage to which the logical volume can grow. Because of the rounding that the system performs internally, the value of this property can be up to 2 GB less than the value for the allocated logical capacity.
- Allocated
- Allocated logical capacity
The amount of storage that the system dedicates to the logical volume. The allocated logical capacity can be any value up to and including the addressable logical capacity. When you create a SAN LUN, you specify this value, which becomes the initial capacity that the system allocates to the LUN.
Tip: If you do not want thin provisioning for the LUN, set the allocated logical capacity equal to the addressable logical capacity.
In contrast, when you create a NAS
filesystem, the allocated logical capacity property is not available. For
filesystems, the
Oracle FS System creates the
filesystem without allocating any initial capacity for the data tiers. Instead, when the
filesystem needs additional capacity, the system automatically allocates the capacity at that time.
Note: The action of the Oracle FS System automatically allocating additional capacity to a thinly provisioned logical volumeis called infill. This additional capacity might not be contiguous with the previous allocations.