8464ch02_Architecture.fm Draft Document for Review February 7, 2020 3:15 pm Replication order TS7700T and TS7700C Replication Handling  Copies are queued at target clusters in the following order: Logical volumes that must be replicated to one or more peer clusters are retained in disk  cache, regardless of their preference group assignments. This feature enables peer clusters  to complete the replication process without requiring a recall. After the copy completes, the  assigned preference group then takes effect. For example, those groups that are assigned as  preference group 0 are then immediately migrated.  If replication is not completing and the retention backlog becomes too large, the original  preference groups are recognized, which enables data that is not yet replicated to be  migrated to tape. These volumes likely must be recalled into disk cache later for replication to  complete. The migration of not yet replicated data might be expected when replication is not  completing because of an extended outage within the grid. Volumes that are written to an I/O TVC that is configured for PG0 have priority by default for  replication to peers. This priority is to help the source cluster flush this data from its cache as  quickly as possible. This behavior overrides a pure FIFO-ordered queue. A new setting is  available in the MI under Copy Policy Override (Ignore cache Preference Groups for copy  priority) to disable this function. When selected, it causes all PG0 and PG1 volumes to be  treated in FIFO order. GLYPH<SM590000> RUN copies GLYPH<SM590000> Synchronous Deferred copies GLYPH<SM590000> RUN deferred copies GLYPH<SM590000> Deferred Copies GLYPH<SM590000> Family Deferred Copies GLYPH<SM590000> COPYRFSH Copies GLYPH<SM590000> How copies from other clusters are treated in the cache GLYPH<SM590000> How recalls are treated in the cache 2.4.21 Expired virtual volumes and the Delete Expired function 2.4.22 TVC management for TS7700T/TS7700C CPx in a multi-cluster grid The Delete Expired function is based on the time that a volume enters the scratch category.  Each cluster in a multi-cluster grid uses the same time to determine whether a volume  becomes a candidate, but each cluster independently chooses from the candidate list when it  deletes data. Therefore, all clusters do not necessarily delete-expire a single volume at the  same time. Instead, a volume that expires is eventually deleted on all clusters within the same  day. Each cluster is limited to a maximum number of deletions per hour. The default is 1,000  per hour, which can be configured in the  LI REQ  command. In addition to the TVC management features from a stand-alone cluster, you can decide the  following information in a multi-cluster grid:  Chapter 2. Architecture, components, and functional characteristics  77