a. On the  Create Mapping  page, select  Host  to display all hosts that are available for  mapping. Hosts must support SCSI unmap commands. Verify that the selected host  type supports SCSI unmap commands. Click  Next . b. Verify the volume, and then click  Map Volumes . 1. To create a Data Reduction Pool, enter the following command: 2. To create a compressed or thin-provisioned volume within a data reduction pool, enter the  following command: 3. To map the volume to a host, enter the following command: 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. To create data reduction on the system, complete these steps:  mkmdiskgrp -name pool_name -ext extent_size -datareduction yes 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. 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. mkvdiskhostmap -host host_name vdisk_name  Where  host_name  is the name of the host and  vdisk_name  is the name of the volume. 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. mkvolume -name name -pool storage_pool_name -size disk_size -compressed mkvolume -name name -pool storage_pool_name -size disk_size -thin Using the command-line interface 4.5.2 Adding external MDisks to existing storage pools Checking access to new MDisks If MDisks are being added to the IBM FlashSystem 9100 cluster, it is probably because you  you want to provide more capacity. In the Easy Tier enabled pools the storage pool balancing  feature guarantees that the newly added MDisks are automatically populated with extents  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, a feature 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: 80  IBM FlashSystem 9200 and 9100 Best Practices and Performance Guidelines