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EMC Symmetrix DMX-3 Product Guide
Symmetrix DMX-3 Input/Output Operations
Symmetrix DMX-3 operation
Intelligent global memory configurations allow Symmetrix DMX-3
disk systems to transfer data at electronic memory speeds that are
much faster than physical disk speeds. Symmetrix systems are based
on the principle that the working set of data at any given time is
relatively small when compared to the total subsystem storage
capacity. When this working set of data is in cache memory, there is a
significant improvement in performance. The performance
improvement achieved depends on both of the following principles:
◆ Locality of reference — If a given piece of information is used,
there is a high probability that a nearby piece of information will
be used shortly thereafter.
◆ Data re-use — If a given piece of information is used, there is a
high probability that it will be re-used shortly thereafter.
These cache memory principles have been used for years on host
systems (CPU and storage devices). Figure 19 on page 102 illustrates
this type of host cache memory use. The cache memory used in this
manner is often a high-speed, high-cost storage unit that functions as
an intermediary between the CPU and main storage.
Figure 19 Host cache use
CPU
Host
Cache
memory
Main
memory
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