SMF Device Allocations By Device Class

MICS provides a number of data elements representing device allocations in the BATPGM, BAT_ST, and BAT_TS files.
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Each observation in these files represents a complete program step, TSO session, or interval if SMF type 30 interval recording is active. The device allocation data elements are derived by counting the number of UNIQUE device addresses encountered in the EXCP segments by device class. The complete set of
MICS
device allocation data elements in the program-level files are:
PGMN3480
Cartridge Tape Devices Allocated
PGMNCOMM
Communication Devices Allocated
PGMNDASD
DASD Devices Allocated
PGMNMDAS
Mountable DASD Devices Allocated
PGMNGRAF
Graphics Devices Allocated
PGMNTAPE
Magnetic Tape Devices Allocated
PGMNUREC
Unit Record Devices Allocated
PGMNVIO
VIO Devices Allocated
and
PGMMXNCA
Max Cartridge Device Allocations
PGMMXNCO
Max Communication Device Allocations
PGMMXNDA
Max DASD Device Allocations
PGMMXNGR
Max Graphic Device Allocations
PGMMXNMD
Max Mountable DASD Device Allocations
PGMMXNTA
Max Tape Device Allocations
PGMMXNUR
Max Unit Record Device Allocations
PGMMXNVI
Max VIO Device Allocations
These data elements represent device allocations by device class. Note that there are two "subclasses" represented: PGMN3480 and PGMMXNCA represent cartridge tape devices only. PGMNTAPE and PGMMXNTA represent all tape devices, including cartridge types. The same is true for PGMNMDAS and PGMMXNMD. These data elements represent mountable DASD only. PGMNDASD and PGMMXNDA represent all DASD devices, including mountable DASD.
The device allocation data elements are grouped into two similar sets. The difference is that the upper set, PGMNxxxx, is
MICS
accumulated data elements, while the lower set, PGMMXNxx, is
MICS
maximum data elements.
At the DETAIL timespan, there is no difference between the accumulated and maximum data elements, unless SMF type 30 interval recording is active. When interval recording is active, and a program step, started task, or TSO session generates more than one interval record, the PGMNxxxx data elements lose much of their value.
If SMF type 30 interval recording is active, PGMNxxxx represents actual device allocations in the first interval of a step only. In the second and later intervals of a step, PGMNxxxx is set to zero if the number of devices is less than or equal to the highest count of devices found in a prior interval. If the number of devices in the current interval is greater than the highest prior number encountered, then PGMNxxxx is set equal to the difference between the current value and the previous high value. Thus, the sum of each PGMNxxxx data element over all intervals of a step will equal the maximum number of CLASS xxxx devices found in any one interval of the step.
Why are the values of the PGMNxxxx data elements changed to zero in the second and later intervals? Because they are accumulated data elements. They are summed to the job-level JOBNxxxx data elements. The algorithm in place to modify the true values of device allocations in the second and greater interval is there to protect clients that charge based on the JOBNxxxx data element values. The switch to SMF type 30 interval recording would significantly increase the value of JOBNxxxx for a job with steps generating multiple interval records per step. This is best described with an example:
A one-step batch job runs for 2 hours and 23 minutes. The job step allocates three 3480 cartridge tape drives and two 3420 round reel tape drives for the duration of the step. SMF type 30 interval recording is not active.
BATPGM file Accumulated Elements| Maximum Elements | PGMN3480 PGMNTAPE | PGMMXNCA PGMMXNTA STEP 1 (02:23) 3 5 | 3 5
Note that PGMN3480 equals PGMMXNCA, and PGMNTAPE equals PGMMXNTA. This is because interval recording is not active.
Now look at the BATPGM observations from the same job with SMF type 30 interval recording active and set for 30-minute intervals.
BATPGM file Accumulated Elements| Maximum Elements | PGMN3480 PGMNTAPE | PGMMXNCA PGMMXNTA INTERVAL 1 (00:30) 3 5 | 3 5 INTERVAL 2 (00:30) 0 0 | 3 5 INTERVAL 3 (00:30) 0 0 | 3 5 INTERVAL 4 (00:30) 0 0 | 3 5 INTERVAL 5 (00:23) 0 0 | 3 5
Note that with interval recording active, the values of PGMN3480 and PGMNTAPE have been set to zero in the second through the fifth intervals. This was done to avoid a dramatic increase in the job-level data elements JOBN3480 and JOBNTAPE. Without the algorithm that modifies the PGMNxxxx data elements in the second and greater intervals, JOBN3480 would have changed from 3 to 15, and JOBNTAPE would have changed from 5 to 25.
The PGMMXNxx data elements should be used by all clients that activate SMF type 30 interval recording.
The following limitations are associated with the PGMMXNxx and PGMNxxxx data elements:
  • These data elements represent unique device addresses allocated by a step or interval. The emphasis is on "allocated." There is no guarantee that the devices were used by the step or session.
  • A single device could be dynamically allocated and used, deallocated, dynamically allocated again and used again, and would only count once in the PGMMXNxx and PGMNxxxx data elements. This is because
    MICS
    only counts each UNIQUE device address once.
  • These data elements do not guarantee nor imply parallel allocation of devices. For example, a PGMMXNTA value of 2 means that two different tape devices were allocated by the step or interval. Both tape devices could have been allocated at the beginning of the step or interval and remained allocated for the duration. Conversely, tape device 1 could have been dynamically allocated, used, and deallocated at the beginning of the step or interval. Tape device 2 could have been dynamically allocated, used, and deallocated at the end of the step or interval. This means that at any given time only one tape drive was allocated by the step or interval, yet the value of PGMMXNTA is 2.
  • A device that is dynamically allocated or deallocated during an interval will count as a PGMMXNxx value for that interval. A deallocated device will be noted as absent in the subsequent interval record.
Dynamic allocation and deallocation of non-sharable devices such as tape drives can increase the effective capacity of the devices at a data center. The ability of
MICS
to determine when the devices were allocated by a job step is hampered because there is no indication of wall clock connect time in the EXCP segments. The activation of SMF type 30 interval records can minimize this uncertainty.
Here is an example:
A one-step batch job runs for 6 hours. The step dynamically allocates six 3480 cartridge tape drives at the beginning of the step. Fifty-five minutes into the step, it deallocates the drives and does not use tape devices again until the final fifty minutes of the step. Five hours and ten minutes into the step, it dynamically allocates four 3480 cartridge tape drives. The device addresses are different from the six devices allocated earlier in the step.
|-------| |-------| | 6 | | 4 | | 3480s |----- No Tape Devices Allocated -----| 3480s | |-------| |-------| |--------|--------|--------|--------|--------|--------| | | Start 1HR 2HR 3HR 4HR 5HR 6HR
This is the observation produced in the BATPGM file without SMF type 30 interval recording:
BATPGM file Accumulated Elements| Maximum Elements | PGMN3480 PGMNTAPE | PGMMXNCA PGMMXNTA Step 1 (06:00) 10 10 | 10 10
Now look at the BATPGM observations from the same job with SMF type 30 interval recording active and set for 60-minute intervals.
BATPGM file Accumulated Elements| Maximum Elements | PGMN3480 PGMNTAPE | PGMMXNCA PGMMXNTA INTERVAL 1 (01:00) 6 6 | 6 6 INTERVAL 2 (01:00) 0 0 | 0 0 INTERVAL 3 (01:00) 0 0 | 0 0 INTERVAL 4 (01:00) 0 0 | 0 0 INTERVAL 5 (01:00) 0 0 | 0 0 INTERVAL 6 (01:00) 0 0 | 4 4
The PGMN3480 and PGMNTAPE data elements are zero in the sixth interval because of the algorithm discussed earlier. Since the four tape drives in the last interval are less than the maximum value in a previous interval, the value of PGMN3480 and PGMNTAPE are changed from four to zero.
It is clear that the maximum data elements contain superior information to aid in device allocation studies at the DETAIL timespan if SMF type 30 interval recording is active. Without interval recording, the maximum and accumulated data elements are identical at the DETAIL timespan.
The data elements representing device allocations in the BATJOB and BAT_JS files are derived from the corresponding program-level elements. These data elements are:
JOBN3480
Cartridge Tape Devices Allocated
JOBNCOMM
Communication Devices Allocated
JOBNDASD
DASD Devices Allocated
JOBNGRAF
Graphics Devices Allocated
JOBNMDAS
Mountable DASD Devices Allocated
JOBNTAPE
Magnetic Tape Devices Allocated
JOBNUREC
Unit Record Devices Allocated
JOBNVIO
VIO Devices Allocated
and
JOBMXNCA
Max Job Cartridge Device Allocations
JOBMXNCO
Max Job Communication Device Allocations
JOBMXNDA
Max Job DASD Device Allocations
JOBMXNGR
Max Job Graphic Device Allocations
JOBMXNMD
Max Job Mountable DASD Device Allocations
JOBMXNTA
Max Job Tape Device Allocations
JOBMXNUR
Max Job Unit Record Device Allocations
JOBMXNVI
Max Job VIO Device Allocations
These job-level data elements are useful for determining jobs that allocate large numbers of devices. The JOBNxxxx data elements are
MICS
accumulated elements. At the DETAIL timespan, they represent the sum of the corresponding PGMNxxxx data elements from all steps of the job. At higher timespans, they represent the sum of all occurrences of JOBNxxxx that were included in the level of summarization.
The JOBMXNxx data elements are
MICS
maximum data elements. At the DETAIL timespan, they represent the maximum value of the corresponding PGMMXNxx data elements from all steps or intervals of the job.
The differences in these accumulated and maximum data elements are best described with an example.
A three-step batch job runs for 25 minutes.
  • Step one allocates three 3480 cartridge tape drives for the duration of the 10-minute step.
  • Step two allocates six 3480 cartridge tape drives for the duration of the 5-minute step.
  • Step three allocates five 3480 cartridge tape drives and three 3420 round reel tape drives for the duration of the 10-minute step.
|---------------------|----------|--------------------| | 3 | 6 | 3 and 5 | | 3480s | 3480s | 3420s 3480s | |---------------------|----------|--------------------| |<---- STEP 1 ------>|<-STEP 2->|<---- STEP 3 ----->|
BATPGM file Accumulated Elements| Maximum Elements | PGMN3480 PGMNTAPE | PGMMXNCA PGMMXNTA Step 1 (00:10) 3 3 | 3 3 Step 2 (00:05) 6 6 | 6 6 Step 3 (00:10) 5 8 | 5 8 BATJOB file | JOBN3480 JOBNTAPE | JOBMXNCA JOBMXNTA Job (00:25) 14 17 | 6 8
The value of JOBN3480 is 14. It is known that 14 cartridge devices were allocated sometime over the three steps of the job. The value of JOBNTAPE is 17. It is known that 17 tape devices (cartridge and round reel) were allocated.
The value of JOBMXNCA is 6. It is known that a maximum of 6 different cartridge devices were allocated in any one interval or step of the job. The value of JOBMXNTA is 8. It is known that a maximum of 8 different tape devices (cartridge and round reel) were allocated in any one interval or step of the job.
The maximum JOBMXNxx data elements provide superior information about device allocation by the steps of the job. A ten-step job with a value of 20 for JOBN3480 could have one step that allocated 20 different cartridge drives, or ten steps that allocated two different cartridge drives each. The value of the JOBMXNCA data element would clear up the mystery.