## Temporary removal threshold 

This process is used in a TS7700 Tape Virtualization multi-cluster grid where automatic removal is enabled and a service outage is expected. Because automatic removal requires validation that one or more copies exist elsewhere within the grid, a cluster outage can prevent a successful check that leads to disk cache full conditions. 

A temporary removal threshold is used to free enough cache space of the TS7700 CP0 cache in advance so that it does not fill up while another TS7700 cluster is in service. This temporary threshold is typically used when plans are made to take down one TS7700 cluster for a considerable amount of time. 

The process is run on the TS7700 MI. 

In addition, the temporary removal threshold can also be used to free up space before a DR test with FlashCopy. During the DR test, no autoremoval or delete expire process is allowed. Therefore, use the temporary removal threshold to ensure that enough free space for the usual productions and the extra flash copies are available in the clusters in the DR family. 

## 2.4.24 TVC management processes in a multi-cluster grid 

The TVC management processes are the same as for stand-alone clusters. In addition to premigration management and free-space management, the following processes are available: 

GLYPH<SM590000> Copy Data Residency Retention (TS7700T/TS7700C CP1 - CP7) 

This process applies to only a multi-cluster grid configuration in which one or more TS7700T/TS7700C clusters exist. TS7700T and TS7700C clusters retain data in disk cache longer than needed if it believes no other peers require a copy. The goal is to reduce recalls for copy. 

After the volume is copied to the required peers, the volume is no longer held in disk cache for this purpose alone and honors its PG0 or PG1 LRU algorithm. If the copies target a remote cluster family, the target family retains the data on behalf of its family peers and the original source cluster is view it as completed. 

This process is done to avoid a possible recall operation from being started by remote clusters in the grid. Only when replication target clusters are known to be unavailable, or when the amount of retained data to be copied becomes excessive, is this retained data migrated ahead of the copy process, which might lead to a future recall to complete the copy. This process is also called copy throttling . 

GLYPH<SM590000> RUN Copy Throttling 

This process applies to multi-cluster grid configurations where the RUN Copy Consistency Point is used. When enabled, it limits the host input rate if it believes the RUN copies cannot keep up otherwise. It is intended to prevent any RUN copies from exceeding the missing-interrupt handler (MIH) timeout value for host jobs. 

If limiting the host input does not help, the job changes to Immediate/RUN Deferred mode and an alert is posted to the host console that the TS7700 entered the Immediate-deferred state. You can modify this setting through the Host Console Request function to customize the level of throttling that is applied to the host input when this condition is detected. In some cases, the RUN Copy throttling can be disabled if high bandwidth and minimal latency between peers exists. Because Synchronous mode copy is treated as Host I/O to the remote cluster, RUN throttling is not applicable to Synchronous copies. 

