Thin provisioning

Thin provisioning defines logical volume sizes that are larger than the capacity installed on the system. The volume allocates capacity on an as-needed basis as a result of host-write actions.

The thin provisioning feature enables the creation of extent space efficient logical volumes. Extent space efficient volumes are supported for FB and CKD volumes and are supported for all Copy Services functionality, including FlashCopy targets where they provide a space efficient FlashCopy capability.

Releasing space on CKD volumes that use thin provisioning

On an IBM Z® host, the DFSMSdss SPACEREL utility can release space from thin provisioned CKD volumes that are used by either Global Copy or Global Mirror.

For Global Copy, space is released on the primary and secondary copies. If the secondary copy is the primary copy of another Global Copy relationship, space is also released on secondary copies of that relationship.

For Global Mirror, space is released on the primary copy after a new consistency group is formed. Space is released on the secondary copy after the next consistency group is formed and a FlashCopy® commit is performed. If the secondary copy is the primary copy of another Global Mirror relationship, space is also released on secondary copies of that relationship.

Note: When the Global Mirror B and C (FlashCopy source and target) volumes are not in the same cluster, space is not released on a thin provisioned Global Mirror C volume during the Global Mirror consistency group formation process.