Chapter 10. Advanced features for storage efficiency 427
Deduplicated volumes cannot coexist in the same I/O group with compressed volumes in 
standard pools. To migrate a compressed volume from a standard pool to a 
thin-provisioned deduplicated or compressed deduplicated volume, a two-step procedure 
is required:
a. For a source compressed volume, create a second compressed, non-deduplicated 
copy in a DRP. Wait for synchronization to complete, and then, delete the source copy.
Complete this process for all compressed volumes in all standard pools in an I/O group 
and verify that no more compressed volumes in standard pools are left.
b. For each compressed volume in a DRP pool, create a second copy on the same DRP 
pool, but select Deduplicated. Wait for synchronization, and delete the source copy to 
complete migration.
Alternatively, right-click a compressed volume in a DRP, click Modify Capacity 
Savings, and select Deduplicated. A second copy is created and the source copy is 
deleted automatically after synchronization completes.
Garbage collection and volume deletion
DRP includes built-in services to enable garbage collection of unused blocks. Garbage 
Collection is a DRP process that reduces the amount of data that is stored on external 
storage systems and internal drives by reclaiming previously used storage resources that are 
no longer needed by host systems.
When a DRP is created, the system monitors the pool for reclaimable capacity from host 
unmap operations. When space is freed from a host operating system, it is a process called 
unmapping. By it, hosts indicate that the allocated capacity is no longer required on a target 
volume. The freed space can be collected and reused on the system, without the reallocation 
of capacity on the storage.
Volume delete is a special case of Unmap that zeros an entire volume. There is a background 
Unmap process that sequentially walks the volume capacity, which emulates large Unmap 
requests. The purpose is to notify the garbage collection technology to free up the physical 
space. 
Because this process can require some time, the volume deletion process in DRPS is 
asynchronous from the command. After you delete a volume by using the GUI or CLI, it goes 
into the deleting state, which can be seen by using the lsvdisk CLI command. After the 
Unmap process completes, the volume disappears.
Both host Unmaps and volume deletions increase unused space capacity. It is displayed by 
the system as reclaimable_capacity, which is shown by using the lsmdiskgrp command, as 
shown in Example 10-10 on page 424. Unused capacity is freed after it is reclaimed by 
garbage collection.
10.5  Compression with standard pools
Random Access Compression Engine (RACE) technology was first introduced in the IBM 
Real-time Compression Appliances. It is integrated into the IBM Storwize V7000 software 
stack as the IBM Real-time Compression (RtC) solution. 
RACE or RtC is used for compression of the volume copies, which are allocated from 
standard pools. DRPs use a different IBM Storwize V7000 compression function.