Chapter 9. Advanced features for storage efficiency 479
Temporal compression adds the time dimension that is not available to other compression
algorithms. It offers a higher compression ratio because the compressed data in a block
represents a more homogeneous set of input data.
Figure 9-30 shows how three writes sent one after the other by a host end up in different
chunks. They get compressed in different chunks because their location in the volume is not
adjacent. This process yields a lower compression ratio because the same data must be
compressed non-natively by using three separate dictionaries.
Figure 9-30 Location-based compression
When the same three writes are sent through RACE, as shown on Figure 9-31, the writes are
compressed together by using a single dictionary. This process yields a higher compression
ratio than location-based compression (Figure 9-31).
Figure 9-31 Temporal compression
9.4.4 Random Access Compression Engine in IBM Spectrum Virtualize stack
RACE technology is implemented into the Storwize thin provisioning layer and is an organic
part of the stack. Compression is transparently integrated with existing system management
design. All of the IBM Storwize V5000 Gen2 advanced features are supported on
compressed volumes. You can create, delete, migrate, map (assign), and unmap (unassign) a
compressed volume as though it were a fully allocated volume.
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