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EMC Symmetrix DMX-3 Product Guide
Performance and Optimization
Each cache partition group (CPG) has its own definable write
pending (WP) limit that can be varied from 40 percent to 80 percent.
As the partition group’s write pending count approaches its write
pending limit, the Symmetrix front-end adapters will introduce “WP
fairness” delays to throttle host write activity. If write activity
continues and the write pending limit is reached, priority destage
operations take place on the Symmetrix back end. If the purpose of
cache partitioning is to contain an application that produces many
writes, then the write pending limit can be set to a premeditated low
value. If operations consistent with the system write pending limit
are desired, this parameter should be left at 80 percent.
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