4.1 Virtualization definition4.2 Abstraction layers for drive virtualization4.2.1 Array sites4.2.2 Arrays4.2.3 Ranks4.2.4 Extent pools4.2.5 Logical volumes4.2.6 Space-efficient volumes4.2.7 Allocation, deletion, and modification of LUNs and CKD volumes4.2.8 Logical subsystems4.2.9 Volume access4.2.10 Virtualization hierarchy summary4.3 Benefits of virtualization