Product manual

CDA 7 5630 Product Manual
4-2 77 A1 69UP Rev00
4.4 Fast Write Capabilities
CDA 7 caches write operations, eliminating the need to write data to the disk
immediately. This results in faster response times and improved overall subsystem
performance. The write ceiling is 80% of the usable cache. Channel directors and
disk directors dynamically allocate cache space between reads and writes
depending on I/O activity.
4.5 Dynamic Mirror Service Policy
The CDA 7 Dynamic Mirror Service Policy (DMSP) is an enhancement to the
adaptive algorithms in the CDA 7 architecture that improves the performance of
read operations in mirrored environments. The improved system performance is a
result of CDA 7 balancing the load between physical disk drives and disk directors,
and minimizing actuator movement.
To achieve this improved performance, CDA 7 measures and tracks I/O activities
of logical volumes, physical volumes and disk directors. Then, based on these
measurements, CDA 7 directs read operations for mirrored data to the appropriate
mirror that results in the best overall performance of the CDA 7 . As the access
patterns and workloads change, the dynamic algorithm analyzes the new workloads
and adjusts the service policies as needed.
4.6 RPS Miss Elimination
In CDA 7, each disk device has a dedicated microprocessor and segmented data
buffer that can temporarily store data until the disk director is ready to read or write
data. This eliminates rotational positional sensing (RPS) misses that occur in
conventional disk device when the heads are positioned over the desired sector, but
the channel path is not ready for read or write operations. The segmented data
buffer of the disk device allows multiple operations to occur to the head/disk
assemblies.
4.7 Channel Speed
CDA 7 Ultra SCSI channels transfer data at speeds up to 40 MB/sec. The data
transfer rate is host dependent. CDA 7 supports cable lengths of up to 82 feet (25
m) to attach to most host systems.