8464ch12_Performance.fm Draft Document for Review February 7, 2020 4:43 pm The TS7700T is not yet reflected in that white paper version. 12.3.2 Grid considerations and replication modes Data can be copied between the clusters by using the Synchronous, RUN (also known as  Immediate ), Deferred Copy, or Time Delayed Copy policy settings. Each of these copy modes  features specific characteristics and influences your RPO for specific application workload.  The chosen copy mode might also have a direct influence on the performance of the TS7700  grid. Although some of the modes enable the copies to be run at a non-peak time (all types of  deferred copies), other copy modes are enforced to run before job end (Synchronous, RUN).  These characteristics of the copy modes imply that resources from the TS7700 (cache  bandwidth, CPU, and grid link bandwidth) must be available now in Synchronous and RUN  copy modes.  The following replication modes are available:  The number of concurrent copy tasks for deferred and RUN copies can be altered by an  authorized user by using a host console Library Request command. When altering the  copy tasks, consider the Grid network configuration and throughput capabilities to make  the best use of the available resources and not over-commit the network or source cluster  for copy activity.  The customer can influence the number of copies for concurrent deferred and RUN  copies, but not for the number of concurrent Synchronous mode copies. In addition,  mechanisms exist to control whether deferred copies are running during peak Host I/O. Be  aware that delaying deferred copies might affect your RPO.  In certain situations, requested Synchronous mode copy or RUN copies cannot be  processed. In this case (depending on your customization), the jobs do not run or they  produce Synchronous-Deferred or Immediate-Deferred copies. These copies are  processed later, when the situation is relieved. For more information about the  Synchronous deferred and Immediate Deferred copies, see 11.8.2, “Handling Replication  Exceptions” on page 696. GLYPH<SM590000> Synchronous mode  means that the data is copied instantly to a second cluster.  Synchronous mode copies occur during the writes from the host, and are synchronized  when a tape sync event occurs. Because of this behavior, synchronous mode copy  features some performance benefits over RUN or deferred copy modes.  GLYPH<SM590000> In  Deferred Copy mode , data is queued for copying, but the copy does not have to occur  before job end. Deferred copy mode allows for a temporarily higher host data rate than  Synchronous or RUN copy mode, and can be useful for meeting peak workload demands.  Consistently exceeding the capacity of your configuration can result in a copy queue,  which cannot be depleted before the next workload peak. Deferred copies are controlled  during heavy host I/O with  Deferred Copy Throttling  (DCT). For more information, see  12.7.6, “Tuning  possibilities for copies: Deferred copy throttling” on page 727.  Typically, when the Rewind Unload (RUN) is sent, the Synchronous copy already  completed. With an immediate copy (RUN), the second copy is not started until the  RUN command is received. In RUN copy mode, the rewind-unload at job end is held up until the  received data is copied to the other cluster (or clusters).  GLYPH<SM590000> The  Time Delayed Replication mode is useful to produce copies to multiple TS7700  clusters only after a predefined timeline expires. This copy mode might reduce the number  of needed copies as no copy is produced at all when the data expires before the  predefined timeline expires; however, the copies can be produced in a different timeline (if  you specify hours after create/access). You cannot specify a specific start. 708  IBM TS7700 Release 5.0 Guide