FCX329, DASD Volume Performance Screen – VOLUME

Performance Toolkit Subcommand: VOLUME.

The DASD Volume Performance Screen (FCX329) shows information about the behavior of DASD volumes.

Figure 1. Layout of DASD Volume Performance Screen (FCX329)

 
FCX329      CPU nnnn  SER nnnnn  Interval HH:MM:SS - HH:MM:SS    Perf. Monitor

.        .      .  .    .     .  ___    .    .    .    .    .    .    .    .    .    .    .     .
<---- Volume ----> LCU    Mdisk           <----- Volume Times (msec) ------> Req. Pct. <-Serv--->
Addr     Label  WA SSID T Links  I/O AIOR Pend Disc Conn Serv Wait Resp CUWt Qued Busy Base Alias
>>Mean>>   1681 .. ...  .   ...  3.0 .019 .252 .591 .744 .216 1.19 .036 .047  .03    4 1.35  13.7
Volume Group Data:
10TPOOL     583 .. ...  .   ...  8.4 .019 .255 .601 .755 .216 1.21 .034 .048  .08   11 1.37  13.7
 
Volume Data:
    C50D ATP111 CP 0607 H     0 22.4    0 .252 11.6 .685 12.5 8.96 21.4    0  .21   28 12.5   ...
    C004 ATP032 CP 0602 H     0 22.3    0 .246 10.8 .698 11.7 7.48 19.2    0  .14   26 11.7   ...
    C701 ATP127 CP 0609 H     0 22.3    0 .251 11.6 .656 12.5 11.6 24.1    0  .27   28 12.5   ...
    C707 ATP133 CP 0609 H     0 22.3    0 .250 11.4 .708 12.4 10.7 23.1    0  .25   28 12.4   ...
    CD05 ATP215 CP 060F H     0 22.3    0 .267 13.4 .694 14.4 13.9 28.3    0  .30   32 14.4   ...
    CD0A ATP220 CP 060F H     0 22.3    0 .257 12.2 .700 13.1 12.1 25.3    0  .27   29 13.1   ...
    C207 ATP063 CP 0604 H     0 22.2    0 .255 11.7 .734 12.7 9.75 22.5    0  .21   28 12.7   ...
    C80A ATP150 CP 060A H     0 22.2    0 .255 11.6 .690 12.5 8.96 21.5    0  .17   28 12.5   ...
    C901 ATP155 CP 060B H     0 22.2    0 .257 11.9 .713 12.9 11.4 24.3    0  .30   29 12.9   ...
    C90A ATP164 CP 060B H     0 22.2    0 .255 11.7 .693 12.6 10.1 22.7    0  .26   28 12.6   ...
    BE00 ATP000 CP 0600 H     0 22.1 .464 .262 12.3 1.45 14.0 .006 14.0 .769    0   31 13.9  14.4
    BF03 ATP017 CP 0601 H     0 22.1    0 .267 13.5 .673 14.4 13.6 28.0    0  .32   32 14.4   ...
    C30A ATP080 CP 0605 H     0 22.1    0 .249 11.0 .698 12.0 8.79 20.8    0  .24   26 12.0   ...




Command ===> _
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Figure 1 shows a screen with DASD volumes sorted in descending order of the I/O rate value, as indicated by the underscore characters above the I/O heading. Other possible sort sequences are indicated by dots above the corresponding columns. These sequences can be set using the SORT subcommand with the string shown in the lowest line of the column heading as the sort argument (see SORT) or by positioning the cursor on the heading of the field that is to be sorted and then pressing ENTER.

Some additional lines with volume group averages are shown at the top when volume groups have been defined. (See FCONTROL DEVGROUP.) In Figure 1, the volume group name (10TPOOL) is displayed in the Addr field, and the number of volumes in the group (583) is displayed in the Label field.

Field Descriptions:

Volume:

Addr

The RDEV number of the volume's base RDEV.

The first line, which contains the prefix >>Mean>> instead of a device number, provides the average load statistics for all volumes for which performance data were collected.

Label

The volume label.

For the >>Mean>> row or for a volume-group row, this column contains the number of volumes.

WA

Indicates where the volume's base RDEV is attached:

CP: Indicates that it is in the CP-owned list.
SY: Indicates that it is attached to SYSTEM.
GU: Indicates that it is attached to a guest.

If the volume is not attached, this field contains dots.

LCU SSID

The subsystem ID (SSID) of the logical control unit (LCU).

T

Indicates the RDEV type for the volume's base RDEV:

P: For a PAV base
H: For a HyperPAV base.

If it is neither a PAV base nor a HyperPAV base, this field contains a dot.

Mdisk Links

The number of minidisk links to the volume.

I/O

The I/O rate. This is the number of SSCH and RSCH operations executed per second to this volume through the base RDEV or any alias RDEV working on behalf of the base during the selected interval.

AIOR

The alias I/O ratio. For each I/O operation performed to the base RDEV, this is the number of I/O operations performed through the alias RDEVs.

Volume Times (msec):

Pend

The "function pending" time. This is the average amount of time that an I/O request remained pending in the I/O subsystem due to path-busy conditions.

This value and the Disc, Conn, Serv, Busy, and Resp values are calculated based on information obtained from the subchannel measurement blocks. Dots are inserted for volumes where the information is not available or is not calculated.

Disc

The "volume disconnected" time. This is the average amount of time that the volume remained disconnected from the channel while executing I/O requests. It includes the time spent on executing the SEEK and SET SECTOR orders and also any re-connect misses. High values could indicate overloaded paths or many long SEEKs to data at opposite ends of the volume.

This value also includes the "device-active-only" time where that information is available.

Conn

The "volume connected" time. This is the average time that the volume was connected to the channel while executing I/O requests, that is, receiving commands or actually transferring data. It also includes the SEARCH time.

Serv

The service time for the volume. This is the sum of the function pending, connected, and disconnected times.

Wait

The volume wait time.

Resp

The volume response time. This is the sum of the service time and the wait time.

CUWt

The control unit queuing time, that is, the additional wait time caused when the target device was already busy with an I/O operation that was started from another system.

Req. Qued

The average I/O queue length in the selected interval.

The value is taken from CP monitor high-frequency sample data; it is an indicator of I/O contention on the volume.

The I/O queue length (Req. Qued) is not meaningful for volumes that are dedicated (attached) to guest systems. The guest system will not try to start another I/O operation before an active one has ended, but rather will do its own queuing. Guest system queuing cannot be shown by host performance monitors, so they will have to be analyzed using a performance monitor on the guest system.

The queue length reported here is the number of real I/O operations (channel programs) that CP's real I/O layer is waiting to start to the device or volume. This includes I/O operations performed for all reasons: for minidisk I/O, for paging I/O, and for spooling I/O, for example. For devices in the CP-owned list, additional queueing information can be found on one of these screens:

Pct. Busy

The percentage of time during which the volume was busy. This value could be greater than 100 if there are alias RDEVs doing work on behalf of the base RDEV.

Serv:

Base: The average amount of service time per I/O operation through the base RDEV to the volume.
Alias: The average amount of service time per I/O operation through an alias RDEV to the volume.

Defining a volume group:

To define a volume group, use FC DEVGROUP. Include only non-PAV DASD RDEVs, PAV base RDEVs, and HyperPAV base RDEVs. Any other types of RDEVs are excluded from the calculation.

The appropriate subset of FC DEVGROUP DASD is used for each volume group.

Effect of AVERAGE and INTERIM subcommands:

Overall or interim period averages will be shown for all load fields. Real averages will be shown for all fields that display device load figures. The Label, WA, LCU SSID, T, and Mdisk Links fields will always contain current information.