Displaying the caching statistics

If you have an IBM® 3990 Storage Control with cache with at least one SMS volume attached, you can display cache statistics, hit ratio, and DASD Fast Write bypasses, by issuing the following command:

D SMS,CACHE

An example of the generated output appears below.

Figure 1. Displaying Cache and DASD Fast Write Information

      IGD002I 09:28:38 DISPLAY SMS 411
        SSID  DEVS  READ  WRITE  HIT RATIO  FW BYPASSES
        0002   32    80    60        68%    62
        0004   14    92   100        76%    30
        000E   20    84   100        84%    44
        0011   08   100   100        92%    16
        001C   08   100   100        86%    24
      ***************************** LEGEND *****************************
      SSID        THE SUBSYSTEM IDENTIFIER OF THE IBM 3990 STORAGE CONTROL
                  MODEL 3 TO WHICH THE INFORMATION APPLIES
      DEVS        THE NUMBER OF SMS-MANAGED DEVICES ATTACHED TO THE IBM 3990
                  STORAGE CONTROL MODEL 3 WITH THIS SSID
      READ        THE PERCENTAGE OF CYLINDERS FOR WHICH DYNAMIC CACHING IS
                  PERMITTED
      WRITE       THE PERCENTAGE OF CYLINDERS FOR WHICH DYNAMIC DASD FAST
                  WRITE IS PERMITTED
      HIT RATIO   THE READ HIT RATIO THAT IS ACHIEVED BY THE IBM 3990 STORAGE
                  CONTROL MODEL 3 WITH THIS SSID
      FW BYPASSES THE NUMBER DASD FAST WRITES PER MINUTE THAT ARE EXECUTED
                  DIRECTLY WITH DASD BECAUSE OF MVS OVER-COMMITMENT

Exception: The read and write percentages are displayed as N/A if the subsystem has the extended platform available. Since the enhanced dynamic cache management algorithm is used, the percentages are no longer valid.