Product manual

CDA 7 Input/Output Operations
77 A1 69UP Rev00 3-5
CDA 7 uses these techniques to enhance its performance:
Split Director Functions The director operations are split into two functional
parts, the channel director and disk director. The
channel director services requests from the host. The
disk director services requests between cache and disk.
Splitting the director functions eliminates the
processing overhead and cache locking associated with
Control Units that perform both functions.
High Speed Cache Memory
Cache memory speed is greater than the total speed of
all components (e.g., the directors) that access it.
Disk Microprocessor and Buffer
Each disk device has its own microprocessor and
buffer. This intelligence is brought to the actuator
level providing parallel processing of data. These
features add another level of caching and improve
overall performance.
Multiple Disk Directors A maximum of 16 disks (CDA 7 models) attach to
each disk director. For more information on director
and disk combinations, refer to Disk Director earlier in
this document.
Sequential Access Patterns
Access patterns can be sequential, random, or a
combination of both. When a miss occurs on a
sequential access pattern, the number of blocks
brought into cache is increased, thus improving the hit
rate (requested data is in cache).