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148 Storage Management with DB2 for OS/390
discarding "foreign overhead" from the target study. However, values related to
this foreign overhead must be preserved because interactions exist on resource
access inside the same computing perimeter. The first step is an overall analysis.
Moreover, this first overview allows locating some missing data and finding
information from other sources. In this case, some input lacking from the RMF
cache analysis reports was compensated by IXFP.
An efficient approach is to build a spreadsheet, doing some consolidation
between the cache subsystem activity and device activity reports. In this case
study, 46 pairs of LCU level RMF reports were reviewed before selecting 9 of
them as relevant. There was no foreign overhead to take into account. Figure 67
on page 148 shows the result of this preliminary step. RMFPP was not used
because we just needed to capture global activities at the LCU and at Storage
Group levels. The report source line is either "crr" for cache activity, "da" for
device activity source, or "crr/da". The fields to review are as follows:
• CUID/ADDR is the CU-ID field of the cache subsystem activity report header
cross-checked with the DEV NUM of the direct access device activity report.
• SSID is the SSID field of the cache subsystem activity report header.
• LCU is the LCU field of the direct access device activity report.
• rmf_rate is the LCU total device activity rate from the direct access device
activity report.
• crr_rate is the aggregate LCU I/O rate field from the cache subsystem device
overview report. These values are higher than the values RMF captured
because control units count at the command level (locate record command)
rather than at the channel program level for RMF. Moreover, there is a missing
value for the two last LCUs because of some operator interaction during the
measurement interval. The fact the "crr" and the "rmf" values are close to each
other shows there is no data sharing with other LPARs.
In most cases, a preknowledge of the environment shortens this pruning process.
Figure 67. Reducing the RMF Data to Analyze
REDUCTION
reports crr/da crr da da crr
field CUID/ADD SSID LCU rate rate
unit ssch / sI/O / sec
RVA_1
1st LCU 2B00 0088 0046 15.8 18.2
2nd LCU 2B40 0089 0047 8.8 10.1
3rd LCU 2B80 008A 0048 14.1 15.9
4th LCU 2BC0 008B 0049 7.9 missing
Tot rva1 46.6 44.200
RVA_2
1st LCU 2C00 2007 004A 3.7 4.2
2nd LCU 2C40 2008 004B 14.4 15.9
3rd LCU 2C80 2009 004C 14.5 16.8
4th LCU 2CC0 200A 004D 11.7 missing
Tot rva2 44.4 36.900
System 71C0 603C 0055 7.0 22.1