428 Implementing the IBM Storwize V7000 with IBM Spectrum Virtualize V8.2.1
For more information about RtC, see IBM Real-time Compression in IBM SAN Volume 
Controller and IBM Storwize V7000, REDP-4859.
10.5.1  Real-time Compression concepts
At a high level, the IBM RACE component compresses data that is written into the storage 
system dynamically. This compression occurs transparently, so Fibre Channel and iSCSI 
connected hosts are not aware of the compression. RACE is an inline compression 
technology, which means that each host write is compressed as it passes through IBM 
Spectrum Virtualize to the disks. This technology has a clear benefit over other compression 
technologies that are post-processing based. 
These technologies do not provide immediate capacity savings. Therefore, they are not a 
good fit for primary storage workloads, such as databases and active data set applications.
RACE is based on the Lempel-Ziv lossless data compression algorithm and operates by 
using a real-time method. When a host sends a write request, the request is acknowledged by 
the write cache of the system, and then staged to the storage pool. As part of its staging, the 
write request passes through the compression engine and is then stored in compressed 
format onto the storage pool. Therefore, writes are acknowledged immediately after they are 
received by the write cache with compression occurring as part of the staging to internal or 
external physical storage.
Capacity is saved when the data is written by the host because the host writes are smaller 
when they are written to the storage pool. IBM RtC is a self-tuning solution that adapts to the 
workload that runs on the system at any particular moment.
10.5.2  Implementing RtC compression
To create a compressed volume, choose Capacity Savings - Compressed in the Create 
Volumes window, as shown in Figure 10-16. For more information about creating volumes, 
see Chapter 7, “Volumes” on page 241.
Figure 10-16   Creating compressed VDisk
In addition to compressing data in real time, you can compress data sets (convert a volume to 
compressed). To do so, you must change the capacity savings settings of the volume by 
right-clicking it and selecting Modify Capacity Settings. In the menu, select Compression 
as the Capacity Savings option, as shown in Figure 10-17 on page 429.