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Case Study 153
12.2.2.2 Cache effectiveness Overall Summary
Figure 73 on page 153 shows an extract of these reports for both RVAs that
contains information similar to RMF, but with more details on caching algorithms,
and also explains the origin of the observed disconnect times. The I/O demand
the host submits to the RVAs and the staging effectiveness are analyzed:
•
Analysis of host I/Os. Both RVAs receive a similar I/O activity demand which is
read-only. That explains the high value of the READ RATIO field, which is the
read-to-write ratio. Moreover, the sum (read-plus-write) is larger than number
of I/Os. There are probably more than one read per I/O.
•
Hit ratios are more than 99%. That is an indication that practically all reads
find their addressed tracks into the cache. This situation is current when a
sequential pre-staging algorithm anticipates the I/O read demand.
•
Staging activity (measured in number of tracks per second) is 2.4 times the I/O
activity:
(113.2 + 103 ) / ( 45.7 + 44.5 ) = 2.4
There are 2.4 tracks staged per I/O:
This intensive staging activity explains the
observed disconnect time
.
Figure 73. Case Study IXFP Cache Effectiveness Overall Extract
12.2.2.3 Space Utilization Summary
Figure 74 on page 154 shows the extracts of space utilization reports for both
RVAs. Table 27 on page 153 summarizes different space utilization by both RVAs.
It also shows how, in this balanced configuration with an evenly distributed
workload and with consistent service times, the NCLs are not homogenous.
Table 27. RVA Space Utilization Comparison
The partitions of the table spaces into RVA 22897 contain data already
compressed by CPU. From performance and transfer bandwidth points of view
(KB per second), both RVAs have similar appeareances.
Subsystem 20395 22897
Net Capacity Load 56.4% 25.2%
% Functional Capacity Stored 28.1 5.4
Compression Ratio 3.1 1.9
XSA/REPORTER CACHE EFFECTIVENESS OVERALL SUMMARY 18FEB1999 17:32:04
SUBSYSTEM NAME: 20395 (CACHE SIZE: 1024 MB NVS SIZE: 8 MB)
SUBSYSTEM READ WRITE I/O READ READ WRITE I/O DFW STAGE HITS/ LOW TRACK
SUMMARY PER SEC PER SEC PER SEC RATIO HIT % HIT % HIT % CONSTR PER SEC STGE REF CT OCCUP
------- ------- ------- ----- ----- ----- ----- ------ ------- ----- ------ ------
PROD PARTITION 53.8 0.0 45.7 61329 99.3 100.0 99.3 0.0 113.2 0.5 73.7
OVERALL TOTALS 53.8 0.0 45.7 61329 99.3 100.0 99.3 0.0 113.2 0.5 73.7 25050
SUBSYSTEM NAME: 22897 (CACHE SIZE: 1280 MB NVS SIZE: 8 MB)
SUBSYSTEM READ WRITE I/O READ READ WRITE I/O DFW STAGE HITS/ LOW TRACK
SUMMARY PER SEC PER SEC PER SEC RATIO HIT % HIT % HIT % CONSTR PER SEC STGE REF CT OCCUP
------- ------- ------- ----- ----- ----- ----- ------ ------- ----- ------ ------
PROD PARTITION 50.1 0.0 44.5 57064 99.9 100.0 99.9 0.0 103.0 0.5 73.5
OVERALL TOTALS 50.1 0.0 44.5 57064 99.9 100.0 99.9 0.0 103.0 0.5 73.5 22086