Workload-based write pacing is an enhanced form of write pacing that uses MVS workload management (WLM). All the concepts of write pacing, described in Write pacing, apply to workload-based write pacing. However, with workload-based write pacing, write pacing is injected at an application level, allowing more than one level of pacing to be active on a single volume at the same time.
Workload-based write pacing uses the importance value on each write I/O to determine the write pacing level to be used in the calculation for how much write pacing delay to inject, if any. The write pacing threshold is used to determine the write pacing step in the same way. To exploit workload-based write pacing, you must enable it on both the application LPAR and the SDM LPAR. On the application LPAR, WLM must be in use. WLM assigns workloads to service classes with the associated importance levels. For information about setting up WLM, refer to z/OS MVS Planning: Workload Management.
Setting up workload-based write pacing
- Set up WLM on the application LPAR.
- Specify STORAGESERVERMGT=YES in the IEAOPTxx member of parmlib on the application LPAR, so that the writes are correctly classified to XRC.
- Specify the WorkloadWritePacing parameter in the XRC parmlib values.
Defining WorkloadWritePacing in parmlib
The WorkloadWritePacing parameter has 6 values corresponding to importance values 1-5 and a discretionary importance value (0). Importance value 1 is the importance value assigned to the SYSTEM service class. Any application that does not have a service class, but is on an LPAR with WLM in use, is assigned to the discretionary importance class. In addition, if XRC is mirroring writes from LPARs that do not support WLM (such as z/Linux or z/VM), or from LPARs that bypass WLM (STORAGESERVERMGT=NO is specified in parnlib member IEAOPTxx), then volume-level pacing is used instead.
DVCBLOCK
Workload-based write pacing changes the behavior of the DVCBLOCK parameter on XADDPAIR and XSET requests.
When workload-based write
pacing is in use, XRC automatically converts DVCBLOCK(ON) to DVCBLOCK(WPn), where n is
the discretionary level, 6.
The value specified with WrtPacingResidualCnt in the XRC parmlib values is used as
the threshold, rather than the value for DeviceBlockingThreshold. Refer to ANTXIN00 parmlib parameters for more information.
For details of DVCBLOCK and workload-based write pacing, refer to Table 1.
| DVCBLOCK Value | Workload-based Write Pacing | Result |
|---|---|---|
| DVCBLOCK(ON) | Enabled in parmlib and all requirements are met | DVCBLOCK(WP6), application level pacing |
| DVCBLOCK(ON) | Enabled in parmlib, WLM disabled or not supported, controller capable | DVCBLOCK(WP6), volume level pacing at discretionary level |
| DVCBLOCK(ON) | Enabled in parmlib, controller incapable | DVCBLOCK(ON), volume device blocking |
| DVCBLOCK(ON) | Not enabled in parmlib | DVCBLOCK(ON), volume device blocking |
| DVCBLOCK(WPn) | Enabled in parmlib and all requirements are met | DVCBLOCK(WPn), application level pacing |
| DVCBLOCK(WPn) | Enabled in parmlib but requirements not met | DVCBLOCK(WPn), volume level pacing at level n |
| DVCBLOCK(WPn) | Not enabled in parmlib | DVCBLOCK(WPn), volume level pacing at level n |
| DVCBLOCK(OFF) or DONOTBLOCK | Enabled in parmlib and all requirements are met | Application level pacing |
| DVCBLOCK(OFF) or DONOTBLOCK | Enabled in parmlib, WLM disabled or not supported, controller capable | No blocking or pacing of volume |
| DVCBLOCK(OFF) or DONOTBLOCK | Enabled in parmlib, controller incapable | No blocking or pacing of volume |
| DVCBLOCK(OFF) or DONOTBLOCK | Not enabled in parmlib | No blocking or pacing of volume |
XQUERY VOLUME PACE
With workload-based write pacing, the XQUERY VOLUME PACE report has several differences:- It is labeled as REPORT 003, rather than REPORT 002
- Lines are added for the statistics of the levels of the write activity within the volumes.
- The values for RES RATE, WRT RATE, and PACE MS on the detail lines are the total values for the volume.
- When workload-based write pacing is in effect for a storage controller, the threshold count (THD CNT) column separator is changed from : to @, and the value after this separator is the setting for the write pacing level from an XADDPAIR or XSET command, not necessarily the level at which the volume is being paced.
- An additional detail line is shown for each WLM pacing level (WLM1-WLM6) that identifies what WLM importance levels are getting written to the volume, and the differentiated pacing in effect.
When workload-based write pacing is disabled (with WorkloadWritePacing in parmlib member ANTXIN00), the report reverts to REPORT 002. For more information, refer to Using XRC reports.
To verify whether a controller is capable of workload-based write pacing, use the XQUERY STORAGECONTROL XFEATURES command instead of the XQUERY STORAGECONTROL FEATURES command. For more information, refer to Using XRC reports.