The Reclaim freed space option in XenCenter enables you to free up unused blocks (for example, deleted virtual disks in an SR) on a LUN that is thinly provisioned by the storage array. Once released, the reclaimed space can then be reused by the array. The Reclaim freed space operation is only available for LVM-based SRs that are thinly provisioned on the array (that is, iSCSI, Fibre Channel, or Local LVM). This feature is not enabled on file-based SRs such as NFS and Ext3 as these SR types do not require a manual space reclamation operation.
To reclaim freed space: