32 Storage Management with DB2 for OS/390
• Simulate potential policy changes and understand the costs of those changes.
• Produce presentation quality charts.
For more informationon the D FSMS/MVS OptimizerFeature, see the following
publications:
•DFSMS Optimizer V1R2 User's Guide and Reference,SC26-7047-04
•DFSMS Optimizer: The New HSM Monitor/Tuner,SG24-5248

4.3.6 SMF Records 42(6)

DFSMS statistics and configurationrecords are recorded in SMF record type 42.
The type 42, subtype 6, SMF record providesinformation about data set level
performance. DFSMS must beactive, but the data set does not need to be SMS
managed. Twoevents cause this record to be generated: data set close time and
each type 30 intervalrecord being written.
Youcan use DFSMSopt or any SMF specialized package to format and display
this useful record. Forinstance, you can start by looking at the list of the first 20
data sets in terms of activity rateat the specified interval and verify that the most
accessed DB2 dataset sare performing as expected both in terms of I/O and
usage of DB2 bufferpools.
Also,accesses to critical data sets can be tracked periodically by data set name.
Their performancecan be mapped against the DB2 PM accounting to determine
detailed characteristics of the I/O executed, and to verify cach e utilization.
4.4 Benefits
A summary of the benefits of SMS follows:
• Simplified data allocation
SMS enables users to simplifytheir data allocations. Without using SMS, a
user would have tospec ifythe unit and volume on which the system should
allocate the data set. In addition, space requirements would need to be
calculated and coded for the data set. With SMS, users can let the system
select the unit, volumeand space allocation. The user therefore, does not
need to know anything about the physicalcharacteristics of the devices in the
installation.
• Improved allocation control
Freespac e requirementscan be set using SMS across a set of disk volumes.
Sufficient levelsof free space can be guaranteed to avoid space abends.The
systemautomatically places data on avolume containing adequate freespace.
• Improved performance
SMS can assist in improving disk I/O performance,and at the same time
reduce the need for manual tuning by definingperformance goals for each
class of data. Cache statistics, recorded in system management facilities
(SMF) in conjunction with the Optimizer feature,can be used to assist in
evaluatingperformance. Sequential data set performance can be improved by
using extended sequential datasets. The DFS MS environmentmakes the
most effective use of the caching abilities of disk technology.