EMC Symmetrix DMX-3, Product Manual

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Disk mirroring (RAID 1) concepts 193
Data Integrity, Availability, and Protection
Dynamic Mirror
Service Policy
(DMSP) The Symmetrix DMSP is a feature of the adaptive algorithms in the
Symmetrix architecture that improves the performance of read
operations in mirrored and Business Continuance Volume (BCV)
environments. The improved system performance is a result of the
Symmetrix system balancing the load between physical disk drives
and disk directors, and minimizing actuator movement.
To achieve this improved performance, the Symmetrix system
measures and tracks I/O activities of logical volumes (including
business continuous volumes), physical volumes, and disk directors.
Then, based on these measurements, the Symmetrix system directs
read operations for mirrored data to the appropriate mirror resulting
in the best overall performance of the Symmetrix system. As the
access patterns and workloads change, the dynamic algorithm
analyzes the new workloads and adjusts the service policies as
needed.
Business
Continuance
Volumes (BCV) A Business Continuance Volume (BCV) is a standard virtual device
(logical volume) used for dynamic mirroring. It has additional
attributes that allow it to independently support host applications
and processes. It may be configured as a single mirror, a locally
mirrored device, or an SRDF source (R1) device. A BCV (virtual)
device can be RAID 1, RAID 5, or SRDF protected.
A business continuance sequence first involves setting, or
establishing, the BCV device as an additional mirror of a standard
device. Once the BCV is established as a mirror of the standard
device, it is not accessible through its original device address. The
BCV device may later be separated, or split, from the standard device
with which it was previously paired. After a split, the BCV device has
valid data and is available for backup or other host processes through
its original device address. Once host processes on the BCV device
are complete, the BCV may again be mirrored to a standard device
(either the same device to which it was previously attached or a
different device). It can then acquire new data for other business
continuance processes or update the standard device with any new
data from the completed business continuance processes.