Where  pool_name  is the name of the pool and  extent_size  is the extent size of the pool.  Data Reduction Pools are created as parent pools only, not child pools. 2. To create a compressed or thin-provisioned volume within a data reduction pool, enter the  following command: Where  name  is the name of the new volume,  storage_pool_name  is the name of the data  reduction pool, and  disk_size  is the capacity of the volume. mkvolume -name name -pool storage_pool_name -size disk_size -compressed mkvolume -name name -pool storage_pool_name -size disk_size -thin 3. To map the volume to a host, enter the following command: mkvdiskhostmap -host host_name vdisk_name Where  host_name  is the name of the host and  vdisk_name  is the name of the volume. For more information, see Creating data reduction pools. Monitor the physical capacity of Data Reduction Pools in the management GUI by selecting  Pools  Pools . In the command-line interface, use the  lsmdiskgrp  command to display the  physical capacity of a data reduction pool. If MDisks are being added to an IBM Spectrum Virtualize or Storwize cluster, this is probably  because you want to provide more capacity. In Easy Tier enabled pools, the storage pool  balancing feature guarantees that the newly added MDisks are automatically populated with  extents coming from the other MDisks, so no manual intervention is required to rebalance the  capacity across the available MDisks. Adding MDisks to storage pools is a simple task, but it is suggested that you perform some  checks in advance especially when adding external MDisks. Be careful when you add external MDisks to existing storage pools to ensure that the  availability of the storage pool is not compromised by adding a faulty MDisk. The reason is  that loss of access to a single MDisk causes the entire storage pool to go offline. In IBM Spectrum Virtualize, there is a feature that tests an MDisk automatically for reliable  read/write access before it is added to a storage pool so that no user action is required. The  test fails under the following conditions: Image-mode MDisks are not tested before they are added to a storage pool because an  offline image-mode MDisk does not take the storage pool offline. Therefore, the suggestion  here is to use a dedicated storage pool for each image mode MDisk. This preferred practice  makes it easier to discover what the MDisk is going to be virtualized as, and reduce the  chance of human error. 106  IBM System Storage SAN Volume Controller, IBM Storwize V7000, and IBM FlashSystem 7200 Best GLYPH<SM590000> One or more nodes cannot access the MDisk through the chosen controller port. GLYPH<SM590000> I/O to the disk does not complete within a reasonable time. GLYPH<SM590000> The SCSI inquiry data that is provided for the disk is incorrect or incomplete. GLYPH<SM590000> The IBM Spectrum Virtualize cluster suffers a software error during the MDisk test. Checking access to new MDisks 3.5.2 Adding external MDisks to existing storage pools