## 4.2.4 Retain Copy mode 

Retain Copy mode is an optional attribute, which is controlled by Management Class construct configuration in which a volume’s prev iously existing Copy Consistency Points are accepted rather than applying the Copy Consistency Points defined at the mounting cluster. This attribute applies to private volume mounts for reads or write appends. It is used to prevent more copies of a volume from being created in the grid than wanted. This attribute is important in a grid with three or more clusters that includes two or more clusters online to a host. 

## 4.2.5 Defining cluster families 

If you have a grid with three or more clusters, you can define cluster families . 

This function introduces a concept of grouping clusters into families. By using cluster families, you can define a common purpose or role to a subset of clusters within a grid configuration. For example, the role that is assigned (production or archive) is used by the TS7700 Licensed Internal Code to make improved decisions for tasks, such as replication and TVC selection. For example, clusters in a common family are favored for TVC selection, or replication can source volumes from other clusters within its family before clusters are used outside of its family. 

## 4.2.6 TS7700 cache thresholds and removal policies 

These thresholds determine the state of the cache as it relates to remaining free space. 

## Cache thresholds for a TS7700 cluster 

There are three thresholds that define the capacity of CP0 in a TS7700T and the active cache capacity in a TS7700D. These thresholds determine the state of the cache as it relates to remaining free space. 

The following thresholds are available in ascending order of occurrence: 

GLYPH<SM590000> Automatic Removal 

The policy removes the oldest logical volumes from the TS7700D and CP0 in TS7700T cache if a consistent copy exists elsewhere in the grid. This state occurs when the cache is 3 TB below the out-of-cache-resources threshold. In the automatic removal state, the TS7700 automatically removes volumes from the disk-only cache to prevent the cache from reaching its maximum capacity. 

This state is identical to the limited-free-cache-space-warning state unless the Temporary Removal Threshold is enabled. You can also lower the removal threshold in the LI REQ. The default is 4 TB. 

To perform removal operations in a TS7700T, the size of CP0 must be at least 10 TB. Consider the following points: 

– You can disable automatic removal within an y specific TS7700D cluster by using the following LIBRARY REQUEST  command, as shown in the following example: 

LIBRARY REQUEST,library-name,CACHE,REMOVE,{ENABLE|DISABLE} 

– The default automatic removal threshold can be changed from the command line by using the following library request command: 

LIBRARY REQUEST,library-name,CACHE,REMVTHR,{VALUE} 

