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## 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 

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. 

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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. 

