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When to use space-reserved LUNs with Snapshot reserve

Space-reserved LUNs and Snapshot copies have space reserved. This reserved space is not available to any other LUNs or Snapshot copies within the volume.

Pre-allocating space for LUNs and Snapshot copies is least efficient in terms of storage utilization because the configured size of the LUN or Snapshot copy reserve could be much larger than what is actually required. You do not need to monitor this configuration as closely as you do thinly provisioned LUNs or LUNs without Snapshot reserve because the space for the LUNs and Snapshot copies is guaranteed for those LUNs and Snapshot copies.

Small installations may benefit from space-reserved LUNs with Snapshot copies because it is often more important to guarantee the space for LUNs and Snapshot copies than to configure for maximum efficiency. For these environments, it is more efficient to guarantee space for a small number of LUNs and Snapshot copies beforehand, which also eases storage system monitoring requirements.

For more information about storage efficiency of space-reserved LUNs with Snapshot reserve, see the technical report TR-3827 on storage efficiency.