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EMC Symmetrix DMX-3 Product Guide
Data Integrity, Availability, and Protection
Note: Symmetrix systems can be configured with dynamic sparing to restore
data protection from a second drive failure. “Dynamic sparing with RAID 5
volumes” on page 219 provides more information on dynamic sparing used
with Symmetrix RAID 5.
RAID 5 performance
optimization
The Enginuity operating environment deploys advanced I/O
optimization techniques to enhance RAID 5 performance on
Symmetrix DMX systems. On sequential writes to a RAID 5 device,
there is no need to read the parity from disk. Since many sequential
tracks are written, they are all in Symmetrix DMX global memory
and hence parity is calculated in memory and is written to disk
without the expensive read-modify-write operation.
Symmetrix Optimizer deployed with RAID 5 on Symmetrix DMX
systems collects statistics on I/O access on individual RAID 5
hypervolumes as well as on RAID 5 devices over extended periods of
time (typically a week). Symm Optimizer provides a comprehensive
analysis of the statistical data collected to identify over-and
under-utilized system resources. For example, Symm Optimizer can
determine if hot spots (places of high I/O activity) or cold spots
(places of low I/O activity) exist. (It is typically observed that 20
percent of physical disks are doing 80 percent of the I/O
activity—Pareto principle.) Symm Optimizer observes and analyzes
this unbalanced workload and makes recommendations for
swapping the hot spindles with the cold spindles. If policy-based
automation is chosen by the customer, Symm Optimizer implements
the recommendations automatically and transparently. This results in
a uniformly distributed workload across all physical spindles which
in turn results in enhanced performance and improved resource
utilization across the entire Symmetrix DMX system.
Note: Symmetrix systems can be configured with dynamic sparing to restore
data protection from a second drive failure. “Dynamic sparing with RAID 5
volumes” on page 219 provides more information on dynamic sparing used
with Symmetrix RAID 5.
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