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Case Study 151
12.2.1.4 Cache Subsystem Activity Reports Analysis
These reports address questions:
1. Is cache overloaded ?
2. What is the efficiency of staging and destaging processes ?
All %READ fields of reports show 100%, so the I/O activity is read-only.
Focus the analysis on LCU 0046, associated with the CU-ID 2B00; refer to Figure
71 on page 151. In the cache subsystem device overview report, the I/O RATE
from the host is 18.2, of which 18.0 are reads and READ H/R is 0.991, which is
good. Moreover, in the CACHE MISSES subset of the CACHE SUBSYSTEM
OVERVIEW, the SEQUENTIAL LINE shows 93457 tracks staged for sequential
prefetch at a rate of 41.1 per second between disk and cache. Those figures
describe well the cache behaviour: intensive sequential read demand, satisfied
by an intensive pre-staging activity with a good hit ratio.
The disconnect time
observed in the device activity report comes from a probable sustained host
demand slightly faster than pre-staging.
This observation can be done on almost every RVA LCU. The CU-ID 2BC0 and
2CC0 show missing data because of a probable operator setting during the test;
IXFP reports should complement it.
Figure 71. Case Study RMF Cache Subsystem Activity Extracts
CACHE SUBSYSTEM ACTIVITY
SUBSYSTEM 3990-03 CU-ID 2B00 SSID 0088 CDATE 02/12/1999 CTIME 15.05.40 CINT 00.37.56
TYPE-MODEL 9393-002
(RMF report extract)
------------------------------------------------------------------------------------------------------------------------------------
CACHE SUBSYSTEM OVERVIEW
------------------------------------------------------------------------------------------------------------------------------------
TOTAL I/O 41324 CACHE I/O 41324 CACHE OFFLINE 0
TOTAL H/R 0.991 CACHE H/R 0.991
CACHE I/O -------------READ I/O REQUESTS------------- ----------------------WRITE I/O REQUESTS---------------------- %
REQUESTS COUNT RATE HITS RATE H/R COUNT RATE FAST RATE HITS RATE H/R READ
NORMAL 892 0.4 547 0.2 0.613 0 0.0 0 0.0 0 0.0 N/A 100.0
SEQUENTIAL 40432 17.8 40392 17.7 0.999 0 0.0 0 0.0 0 0.0 N/A 100.0
CFW DATA 0 0.0 0 0.0 N/A 0 0.0 0 0.0 0 0.0 N/A N/A
TOTAL 41324 18.2 40939 18.0 0.991 0 0.0 0 0.0 0 0.0 N/A 100.0
------------------------CACHE MISSES----------------------- ------------MISC------------ ------NON-CACHE I/O-----
REQUESTS READ RATE WRITE RATE TRACKS RATE COUNT RATE COUNT RATE
DFW BYPASS 0 0.0 ICL 0 0.0
NORMAL 345 0.2 0 0.0 385 0.2 CFW BYPASS 0 0.0 BYPASS 0 0.0
SEQUENTIAL 40 0.0 0 0.0 93457 41.1 DFW INHIBIT 0 0.0 TOTAL 0 0.0
CFW DATA 0 0.0 0 0.0 ASYNC (TRKS) 0 0.0
TOTAL 385 RATE 0.2
----CKD STATISTICS--- ---RECORD CACHING---
WRITE 0 READ MISSES 0
WRITE HITS 0 WRITE PROM 0
-----------------------------------------------------------------------------------------------------------------------------------
CACHE SUBSYSTEM DEVICE OVERVIEW
-----------------------------------------------------------------------------------------------------------------------------------
VOLUME DEV DUAL % I/O ---CACHE HIT RATE-- ----------DASD I/O RATE---------- ASYNC TOTAL READ WRITE %
SERIAL NUM COPY I/O RATE READ DFW CFW STAGE DFWBP ICL BYP OTHER RATE H/R H/R H/R READ
*ALL 100.0 18.2 18.0 0.0 0.0 0.2 0.0 0.0 0.0 0.0 0.0 0.991 0.991 N/A 100.0
*