Draft Document for Review February 7, 2020 4:43 pm 8464ch12_Performance.fm Decrease the copy count  12.7.5 Tuning to avoid the throttling Decreasing the copy count can be beneficial in the following situations:  Several tuning possibilities can be considered for the different types and reasons for throttling. Some of these reasons are the result of parameter changes (PMTHLVL adjustments or  ICOPYT); other issues can be solved only by providing higher bandwidth or more resources  (cache or drives). Although adjusting a parameter might be beneficial for a specific situation, it might affect other  behaviors in the grid. Therefore, we recommend discussing such tuning measurements with  your IBM representative. We describe a common tuning action next. GLYPH<SM590000> If you have limited network bandwidth (for example, less than the 100 MiBps).  GLYPH<SM590000> If the bandwidth is limited and running too many copies in parallel prolongs the single copy  time. This issue can result in timeouts. When you cross this threshold, the system  switches from RUN to IMMED-Deferred. For a deferred copy, the copy is deleted from the  copy tasks and is scheduled back to the copy queue. GLYPH<SM590000> If packet loss is reported and a hardware issue or the grid link quality is not the reason.  GLYPH<SM590000> If too many copies are running in parallel, a single copy stream might run into a packet  timeout, which is reported as packet loss. Disabling host write throttle because of immediate copy Host write throttle can be turned on because of immediate copies taking too long to copy to  other clusters in the grid. Host write throttling is applied for various reasons, including when  the oldest copy in the queue is 20 or more minutes old. The TS7700 changes an immediate  copy to immediate-deferred if the immediate copy is not started after 40 minutes in the  immediate copy queue. The reason for this approach is to avoid triggering the 45-minute missing interrupt handler  (MIH) on the host. When a copy is changed to immediate-deferred, the RUN task is  completed, and the immediate copy becomes a high priority deferred copy. For more  information, see 11.8.2, “Handling Replication Exceptions” on page 696. You might decide to turn off host write throttling because of immediate copies taking too long  (if having the immediate copies take longer is acceptable). However, avoid the 40-minute limit  where the immediate copies are changed to immediate-deferred. In grids where a large portion of the copies is immediate, better overall performance was  observed when the host write throttled because immediate copies is turned off. You are  trading off host I/O for the length of time that is required to complete an immediate copy.  For more information about enabling and disabling host write throttle because of immediate  copies, see  IBM Virtualization Engine TS7700 Series z/OS Host Command Line Request  User’s Guide , which is available at the IBM Techdocs web page. Use the keywords SETTING,  THROTTLE, ICOPYT. 726  IBM TS7700 Release 5.0 Guide