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EMC Symmetrix DMX-3 Product Guide
Performance and Optimization
Fast write
capabilities
Symmetrix systems process all write operations in global memory,
eliminating the need to write data to the disk immediately. This
capability results in faster response times and improved overall
subsystem performance. Channel directors and disk directors
dynamically allocate global memory space between reads and writes,
depending on I/O activity.
Dynamic Mirror
Service Policy
(DMSP) algorithm
When implementing mirroring (RAID 1) data protection in
Symmetrix systems, DMSP determines which of the mirrors of a
given logical volume should service a read miss (when the data is not
found in global memory) operation. Attached BCVs can also
participate in the DMSP. DMSP provides a dynamic approach to
setting the optimal mirror service policy. The DMSP algorithm
monitors the access patterns to the different logical volumes in the
Symmetrix back end and, based on this, determines a policy for the
next few minutes. The DMSP tries to achieve two goals:
◆ Balance the load among all of Symmetrix back-end components.
◆ Minimize the seek time spent on the physical drives.
Note: DMSP also works with the Symmetrix file system as described in
“Enhancement of dynamic mirror service policy” on page 122.
Disk Rotational
Position Ordering
(RPO)
Disk Rotational Position Ordering (RPO) optimization can more than
double the number of random I/Os a disk can do. Whenever
multiple I/O requests are queued on the disk, the EMC Enginuity
Operating Environment can optimize the order in which the I/Os are
executed. The RPO optimization reorders the I/Os based on their
physical location on the drive. RPO optimization significantly
reduces the effect of seeks and latency times on the overall
performance of the disk. To take full advantage of the RPO
optimization, the Symmetrix system needs to queue enough I/Os on
the physical drives. The more I/O demand the Symmetrix system
encounters, the better it will perform.
Disk Multiple Priority
Queues (DMPQ)
Disk Multiple Priority Queues enable the Symmetrix system to give
better response times to I/Os that the hosts are waiting for, without
sacrificing the disk RPO optimization. The multiple-priority queues
algorithm handles starvation situations, so even the low priority I/Os
are serviced within a time-optimized period.
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