8464ch02_Architecture.fm Draft Document for Review February 7, 2020 3:15 pm The takeover mode for the unavailable cluster remains in place until another mode is  selected or the unavailable cluster is restored. Only one available cluster must enable the  takeover mode because all peers share the enablement after it is enabled. GLYPH<SM590000> Write Ownership Takeover (WOT) When WOT is enabled for an unavailable cluster, ownership of a volume is taken from the  unavailable TS7700 Cluster when the volume is accessed. Full access is allowed through  the requesting TS7700 Cluster in the grid and all other available TS7700 clusters in the  grid. The mode for the unavailable cluster remains in place until another mode is selected or the  failed cluster is restored. If volumes were taken over with the read-only takeover mode,  enabling write ownership takeover allows any previous takeovers and future takeovers to  enable updates. Scratch mounts continue to prefer volumes that are owned by the available clusters. Only  after all available candidates are exhausted does it take over a scratch volume from the  unavailable cluster. You can set the level of ownership takeover, Read-only or Write, through the TS7700 MI or LI  REQ. More than one cluster can have ownership takeover enabled. For example, if two clusters  both become unavailable, ownership takeover must be enabled against both clusters  individually so that the remaining cluster or clusters can access volumes that are owned by  the two unavailable clusters. Important:  You cannot change the takeover mode of a cluster in service.  For more information about an automatic takeover, see 2.4.33, “Autonomic Ownership  Takeover Manager” on page 92. All vNodes in a grid feature direct access to all logical volumes in the grid. The cluster that is  selected for the mount is not necessarily the cluster that is chosen for I/O TVC selection. All  I/O operations that are associated with the virtual tape drive are routed to and from its vNode  to the I/O TVC. When a TVC that is different from the local TVC at the actual mount point is chosen, this  mount is called a  remote mount.  The TVC is then accessed by the grid network. Selecting the  TVC can be influenced by using several methods.  During the logical volume mount process, the best TVC for your requirements is selected  based on the following considerations:  2.4.4 I/O TVC selection  GLYPH<SM590000> Availability of the cluster GLYPH<SM590000> Copy Consistency policies and settings GLYPH<SM590000> Scratch allocation assistance (SAA) for scratch mount processing GLYPH<SM590000> DAA for specific mounts  GLYPH<SM590000> Override settings GLYPH<SM590000> Cluster family definitions GLYPH<SM590000> Disk cache residency and recall times GLYPH<SM590000> Network latency times 64  IBM TS7700 Release 5.0 Guide