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 . 

## Using the command-line interface 

To create data reduction on the system, complete these steps: 

1. To create a Data Reduction Pool, enter the following command: 

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. 

2. To create a compressed or thin-provisioned volume within a data reduction pool, enter the following command: 

mkvolume -name name -pool storage_pool_name -size disk_size -compressed mkvolume -name name -pool storage_pool_name -size disk_size -thin 

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. 

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. 

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. 

## 4.5.2 Adding external MDisks to existing storage pools 

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. 

## Checking access to new 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: 

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. 

