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Millisecond response time and cache management z/OS DFSMSdfp Storage Administration SC23-6860-01 |
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At run time, when control unit caching is available, data is divided into three categories: must cache, may cache, and never cache. Dynamic data set cache management is an SMS feature that permits expanded use of a storage controller that supports dynamic cache management enhancement (DCME) with cache, caching and DASD fast write features when these features are under-used or provides restricted use when they are overused. Only system-managed data sets that reside on volumes attached through a storage controller that supports DCME with cache are affected. Data sets not managed by SMS and data sets that reside on volumes attached through storage controls other than a storage controller that supports DCME with cache are not affected. Dynamic cache management improves performance when a storage controller that supports DCME with cache is overloaded. It implements a cache management algorithm that optimizes the selection of data sets that are cache candidates. This enhancement also prevents over-commitment of nonvolatile storage. New I/O statistics by data set and SMS storage class can be collected and monitored by using the System Management Facility (SMF). Refer to z/OS MVS System Management Facilities (SMF) for details on the structure of SMF type 42 records. As a function of dynamic data
set cache management, each system-managed
data set is assigned a cache usage attribute and a DASD fast write
usage attribute for sequential and direct accessing modes. These usage
attributes are based on the MSR and bias specifications found in the
storage classes associated with the data set. These attributes are:
Recommendation: Direct your IDCAMS
query regarding the status of cache/DFW to the controller, because
querying the device can lead to incorrect conclusions.
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