A thin-provisioned volume can be converted nondisruptively to a fully allocated volume, or  vice versa, by using the Modify Capacity Savings functions. Figure 5-5 shows how to convert  volume type. You can right click on the volume and select Modify Capacity Savings. Figure 5-5 Converting volume types nondisruptively The fully allocated to thin-provisioned migration procedure uses a zero-detection algorithm so  that grains that contain all zeros do not cause any real capacity to be used. Tip:  Consider the use of thin-provisioned volumes as targets in FlashCopy relationships. When you create volumes, you can specify compression as a method to save capacity for the  volume. With compressed volumes, data is compressed as it is written to disk, saving more  space. When data is read to hosts, the data is decompressed.  Compression is available through data reduction support as part of the system. If you want  volumes to use compression as part of data reduction support, compressed volumes must  belong to data reduction pools. Data reduction pools also support reclaiming unused capacity  automatically after mapped hosts no longer need the capacity for operations.  These host issue SCSI unmap commands and the released capacity is reclaimed by the data  reduction pool for redistribution. For compressed volumes in data reduction pools, the used  capacity before compression indicates the total amount of data that is written to volume  copies in the storage pool before data reduction occurs. This compression solution provides nondisruptive conversion between compressed and  uncompressed volumes and eliminates the need for special procedures to deal with  compressed volumes. If you are planning to virtualize volumes that are connected to your hosts directly from any  storage subsystems, and you want to know what the space saving you will achieve run the  Comprestimator Utility. Comprestimator is a command-line, host-based utility that can be used to estimate an  expected compression rate for block devices. The previous link provides all of the instructions  needed. 5.3.1 Compressed volumes Chapter 5. Volumes  109