10.5.1 Real-time Compression concepts 10.5.2 Implementing RtC 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. 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 263. In addition to compressing data in real time, you can compress data sets (convert volume to  compressed). For this conversion, 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 453. 452  Implementing the IBM System Storage SAN Volume Controller with IBM Spectrum Virtualize V8.2.1 Figure 10-16 Creating compressed VDisk