CACHDBSE
Purpose
The CACHDBSE subcommand causes the CU-Cached Disks Screen (FCX111) to be displayed.
Format
Parameters
No parameters are allowed or tested for.
Usage
- The whole analysis is based on counters which are updated within
the cached control units. These counters reflect the load and behavior
of specific disks, but they do not tell where the I/O
came from. If several systems share a device, the total of
all activity on the disk is displayed, and not just
the I/Os from the system which is doing the analysis.
The same problem exists for systems which are running second level – an analysis by the second level system will include any I/O activity to the same devices from the first level system.
- Second level systems may face an additional problem: since they only have one path to each device, they will retrieve data only from one cached control unit director. If a device is connected to the first level system over two paths and two different control units (e.g. 3880-23), the first level system may pass the data retrieval request randomly to either of the two control unit directors. Figures obtained by the second level system in this way will tend to be reasonably correct in the long run, but cannot be relied on for single intervals.