Space-efficient storage commands

Edit online

Space-effiicient storage commands create, modify, delete, and display extent space-efficient (ESE) and track space-efficient (TSE) repositories. These two types of repositories differ in many ways, but the main idea of a repository is identical.

A repository of type T and of capacity N guarantees that at least N bytes are available in the extent pool to provision the defined virtual T volumes. This configuration means that other types of non-T allocations will not consume all of the available storage in the extent pool. It also guarantees that no more than N bytes from the extent pool will be used to provision the defined virtual T volumes. Therefore, T allocations will not consume all of the available storage in the extent pool.

A repository also provides a clear and intuitive definition for the over-provisioned ratio, also known as the over-allocation or over-commitment ratio. The over-provisioned ratio is the sum of all the virtual T volume capacities divided by the repository capacity N. In other words, for any fixed repository capacity, the over-provisioned ratio varies only with virtual T volume creations and deletions. The ratio does not vary with any virtual non-T volume creations and deletions.

Although ESE volumes previously existed, the DS8000® system did not allow the creation of an ESE repository until Release 7.2. Without an ESE repository, no method to reserve storage to provision ESE volumes was available. Also, no method to prevent the ESE volume allocations from consuming the entire extent pool was available. Both problems were solved with the creation of an ESE repository, which is similar in effect to a TSE repository. However, the underlying mechanism to provide an ESE repository and the mechanism to provide a TSE repository are completely different.

Note: Track space-efficient (TSE) repositories are required to create TSE volumes. However, starting with DS8000 Release 8, TSE repositories can no longer be created.

For TSE repositories:

All storage used to provision TSE volumes is physically allocated at repository-creation time.
A TSE repository is required to create TSE volumes.
The minimum TSE repository capacity is 16 GiB/Mod1.
Changing the capacity size of an existing TSE repository is not supported.
Changing the extent pool capacity does not affect the TSE repository capacity (capacity is fixed).
All TSE volumes must be removed before attempting to remove the TSE repository.

For ESE repositories:

All storage used to provision ESE volumes is physically allocated at volume-creation time.
An ESE repository is not required to create ESE volumes.
The minimum ESE repository capacity is 0 GiB/Mod1.
Changing the capacity size of an existing TSE repository is supported.
Changing the extent pool capacity does affect the ESE repository capacity (percentage is fixed).
Any existing ESE volumes need not be removed before attempting to remove the ESE repository. The existing volumes remain unchanged after the repository is removed.

The following space-efficient storage commands are available:

chsestg: Modifies the attributes of the specified repository in an extent pool.
lssestg: Generates a report that displays the repository values for the entire storage image.
mksestg: Creates the specified repository in an extent pool.
rmsestg: Deletes the specified repository from an extent pool.
showsestg: Generates a report that displays the detailed properties of the specified repository in an individual extent pool.