8464ch02_Architecture.fm Draft Document for Review February 7, 2020 3:15 pm For more information, see  IBM TS7700 Series Grid Resiliency Improvements User’s Guide ,  WP102742. 2.4.37 Service preparation mode The transition of a cluster into service mode is called  service prep . Service prep enables a  cluster to be gracefully and temporarily removed as an active member of the grid. The  remaining sites can acquire ownership of the volumes while the cluster is in service. If a  volume that is owned by the service cluster is not accessed during the outage, ownership is  retained by the original service cluster. Operations that target the distributed library that is  entering service are completed by the site going into service before the move to service  completes.  Other distributed libraries within the composite library remain available. The host device  addresses that are associated with the site in service send Device State Change alerts to the  host enabling those logical devices that are associated with the service preparation cluster to  enter the  pending offline  state.  If a cluster enters service prep, the following copy actions are processed:  GLYPH<SM590000> All copies in flight (running currently), regardless of whether they are going to or from the  cluster, are finished. GLYPH<SM590000> No new copies from other clusters to the cluster that is entering the service mode are  started. GLYPH<SM590000> All logical volumes that are consistent only on the service prep cluster and require at least  one peer copy are copied to at least one other cluster in the grid. This is true for all copies  except those that are Time Delayed.  GLYPH<SM590000> For time delayed copies, all data that should be copied in the next 8 hours to the target  clusters is copied. All other data is not copied, even if the data is only in the cluster that is  entering the service mode.  GLYPH<SM590000> Any pending updates (hot tokens) to peer clusters where the service-prep cluster is the  current owner must be reconciled or the volume ownership must be transferred to an  available peer. When service prep completes and the cluster enters service mode, nodes at the site in  service mode remain online. However, the clusters are prevented from communicating with  other sites. This stoppage enables service personnel to run maintenance tasks on the site’s  nodes, run hardware diagnostics, and so on, without affecting other sites. Only one service prep can occur within a composite library at a time. If a second service prep  is attempted while another cluster is still in service prep, the second request fails. You should  put only one cluster in the service prep mode at the same time. After service prep completes,  another cluster can then be put into service prep.  98  IBM TS7700 Release 5.0 Guide