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## 1.7.2 Thin provisioning 

Volumes can be configured to be thin-provisioned  or fully allocated . A thin-provisioned volume behaves as though it were a fully allocated volume in terms of read/write I/O. However, when a volume is created, the user specifies two capacities: the real capacity of the volume and its virtual capacity. 

The real capacity determines the quantity of MDisk extents that are allocated for the volume. The virtual capacity  is the capacity of the volume that is reported to IBM Storwize V5000 Gen2 and to the host servers. 

The real capacity is used to store the user data and the metadata for the thin-provisioned volume. The real capacity can be specified as an absolute value or a percentage of the virtual capacity. 

The Thin Provisioning feature can be used on its own to create over-allocated volumes, or it can be used with FlashCopy. Thin-provisioned volumes also can be used with the mirrored volume feature. 

