Virtual Storage - Cost Savings and ROI

Full Use: Space Reclamation for Thinly Provisioned Storage
Both SANmelody and SANsymphony offer the choice to thinly provision virtual disks rather than tie up physical capacity when LUNs are first created. This is particularly desirable with virtual machines that generally consume only a small fraction of the total volume assigned to them. With DataCore, once-occupied, thinly provisioned space will be automatically reclaimed in the background after applications or file systems zero it out. In this way, the SAN gives back capacity that may have been temporarily needed, further optimizing resource utilization.
http://www.datacore.com/solutions/thin_provisioning.asp