6. DATA SOURCES › 6.6 I/O Measurements and Device Activity › 6.6.4 Device Activity And Utilization › 6.6.4.3 Device Allocations By Device Class
6.6.4.3 Device Allocations By Device Class
CA MICS provides a number of data elements representing
device allocations in the BATPGM, BAT_ST, and BAT_TS files.
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 CA 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 CA MICS accumulated data elements, while the
lower set, PGMMXNxx, is CA 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:
o 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.
o 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 CA MICS only counts each
UNIQUE device address once.
o 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.
o 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 CA 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 CA 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 CA 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.
o Step one allocates three 3480 cartridge tape drives for
the duration of the 10-minute step.
o Step two allocates six 3480 cartridge tape drives for the
duration of the 5-minute step.
o 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.
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