8464ch04_Planning.fm Draft Document for Review February 7, 2020 3:15 pm During normal operation of a TS7700 grid configuration, logical volume mount requests  can be satisfied from the local TVC or a remote TVC. TS7700 algorithms can evaluate the  mount request and determine the most effective way to satisfy the request from within the  TS7700 grid.  If the  local  TVC does not have a current copy of the logical volume and a remote TVC  does, the TS7700 can satisfy the mount request through the grid by accessing the volume  in the TVC of a  remote  TS7700. The result is that in a multicluster configuration, the grid  combines the TS7700 TVCs to produce a larger effective cache size for logical mount  request. Notes:  Consider the following points: When a program issues a scratch mount to write data, the TS7700 completes the mount  request without having to recall the logical volume into the cache. With the TS7700D, all  mounts are cache hit mounts. For workloads that create many tapes, scratch mount  significantly reduces volume processing times and improves batch window efficiencies.  The effect of the use of the scratch category on the TVC improves mount performance in  the TS7700T because no physical mount is required. The performance for scratch mounts  is the same as for TVC read hits.  Scratch mount times are further reduced when the optimal scratch allocation assistance  function is enabled. This function designates one or more clusters as preferred candidates  for scratch mounts by using a Management Class construct that is defined from the  TS7700 Management Interface. The comparison between the time that is taken to process  a mount request on a subsystem with cache to a subsystem without cache is shown in  Figure 4-9 on page 194. GLYPH<SM590000> The term  local  refers to the TS7700 cluster that is running the logical mount to  the host.  GLYPH<SM590000> The term  remote  refers to any other TS7700 that is participating in the same grid as  the local cluster. GLYPH<SM590000> Scratch mount times GLYPH<SM590000> Disaster recovery GLYPH<SM590000> Multifile volumes The TS7700 grid configuration is a perfect integrated solution for disaster recovery data.  The TS7700 clusters in a multi-cluster grid can be separated over long distances and  interconnected by using a TCP/IP infrastructure to provide for automatic data replication.  Data that is written to a local TS7700 is accessible at the remote TS7700 as though it  were created there. Flexible replication policies make it easy to tailor the replication of the  data to your business needs.  The Copy Export function provides another disaster recovery (DR) method. The  copy-exported physical volumes can be used in an empty TS7700 to recover from a  disaster or merged into an existing TS7700 grid. For more information, see 2.3.14, “Copy  Export function” on page 53. Stack multiple files onto volumes by using JCL constructs, or by using other methods, to  better use cartridge capacity. Automatic use of physical cartridge capacity is one of the  primary attributes of the TS7700T. Therefore, in many cases, manual stacking of data sets  onto volumes is no longer required. If you are planning for a new application that uses JCL  to stack data sets onto a volume, the TS7700T makes this JCL step unnecessary.  Chapter 4. Preinstallation planning and sizing  195