Product guide

Virtual Provisioning overview 257
About Virtual Provisioning
How Virtual Provisioning works
Storage allocation operations are performed in thin device extents. A round-robin
mechanism balances the allocation of data device extents across all of the data
devices in the pool that are enabled and that have unused capacity. The initial bind of
a thin device to a pool causes one thin device extent, or 12 tracks (768 KB), to be
allocated per thin device. When a read is performed on a thin device, the data being
read is retrieved from the appropriate data device in the storage pool to which the thin
device is bound. Reads directed to an area of a thin device that has not been mapped
do not trigger allocation operations. The result of reading an unmapped block is that a
block in which each byte is equal to zero will be returned. When a write to a thin
device is serviced, storage is allocated to the thin device from the data devices in the
associated storage pool. When more storage is required, data devices can be added
to existing thin storage pools. New thin devices can also be created and associated
with existing thin pools.
It is possible for a thin device to be presented for host use before all of the reported
capacity of the device has been mapped. It is also possible for the sum of the
reported capacities of the thin devices using a given pool to exceed the available
storage capacity of the pool. Such a thin device configuration is said to be
“oversubscribed.”
Unbinding a thin device from a pool frees all the space that the thin device had
consumed from that pool. The data cannot be recovered after the thin device is
unbound.
Supported Symmetrix arrays
Virtual Provisioning is supported in EMC Ionix ControlCenter 6.1 for Symmetrix DMX-3
or DMX-4 storage arrays with Enginuity 5773 or Symmetrix V-Max storage arrays with
Enginuity 5874. It requires the Symmetrix Management Console (SMC) version 6.1 or
later and Solutions Enabler 6.5.0 or later.