8464ch02_Architecture.fm Draft Document for Review February 7, 2020 3:15 pm 2.3.3 Resident-only TVC cache management 2.3.4 Premigration of CPx TVC content In a stand-alone disk-only TS7700D, virtual volumes always remain in the TVC because no  physical tape or cloud is attached. In a TS7700T and TS7700C configuration, contents in the  CP0 partition are also not candidates for moving to physical tape or cloud. Lastly, a DS8000  object partition retains all objects in disk cache and does not yet support movement to  physical tape or cloud. For virtual volumes in this state, only Delete Expire processing, a  logical volume EJECT, or a reuse can free up the logical volume TVC space.  For a DS8000 Object partition, SMS-initiated object deletes free up the space for the  offloaded object by requesting an attached DS8000 to delete the object and any metadata  objects that is associated with it. In a TS7700T or TS7700C,  LI REQ PARTRFSH  can be used to  move resident-only volumes from CP0 to a CPx partition as another method to free up CP0  capacity. If a disk-only TS7700D or resident-only partition begins to run out of space, warning  messages are surfaced to all attached hosts and the library enters a degraded state. If  capacity continues to grow and the free space is exhausted, a critical message is surfaced  and the TS7700D or resident-only partitions enter a read-only state. The TS7700D enters the  Out of Cache condition and moves to a read-only state. If a TS7720T/TS7760C CP0 partition  becomes full, it becomes read-only regarding workloads that target CP0. Important:  Monitor your cache in a TS7700D stand-alone environment to avoid an Out of  Cache Resources situation. The TS7700T and TS7700C support the ability to automatically offload logical volumes from  TVC cache to back-end attached tape or cloud.  Premigration  is the term that is used for  putting logical volumes onto a physical tape or object store. The next few sections describe  how this premigration process works.  You can specify 1 - 7 independent disk cache partitions (CPx). Each partition features its own  independent cache management that allows different workloads to have different disk cache  footprint characteristics. For example, workloads that benefit from a high disk cache hit ratios  can use a large disk cache partition, while those workloads that are rarely accessed and  benefit little from disk cache residency can use a smaller disk cache partition.  Premigration with multiple disk cache partitions By providing each workload type its own partition, the hierarchical storage management  concepts can apply to other volumes with similar workload characteristics only.  The Storage Group (SG) construct is used to determine which partition a workload targets.  After it is in a CPx partition, it is then a candidate for premigration or the copying to back-end  tape or cloud. By default, the queuing of the premigration occurs within minutes of volume  close. But, it can be delayed by using Time-delayed premigration. The total amount of logical volume content that can be queued for premigration to tape or  cloud is limited by the number of FC 5274 and FC 5279 features. The  LI REQ PMTHLVL  value is  used to determine when the TS7700T or TS7700C begins to slow down inbound host activity  to prevent the premigration queue from growing much further. This concept is referred to as  Host Throttling  and is a normal behavior for the TS7700T and TS7700C.  42  IBM TS7700 Release 5.0 Guide