In ascending order of occurrence, the following thresholds are available: 

GLYPH<SM590000> Automatic Removal 

The policy removes the oldest logical volumes from the disk-only TS7700 cache if a consistent copy exists elsewhere in the grid. This state occurs when the cache is 4 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. 

Automatic removal can be disabled within any specific TS7700 cluster by using the following library request command: 

LIBRARY REQUEST,CACHE,REMOVE,{ENABLE|DISABLE} 

Automatic removal is temporarily disabled while disaster recovery write protect is enabled on a disk-only cluster so that a disaster recovery test can access all production host-written volumes. When the write protect state is lifted, automatic removal returns to normal operation. 

GLYPH<SM590000> Limited free cache space warning 

This state occurs when less than 3 TB of free space remains in the cache. After the cache passes this threshold and enters the limited-free-cache-space-warning state, write operations can use only an extra 2 TB before the out-of-cache-resources state is encountered. 

When a TS7700 cluster enters the limited-free-cache-space-warning state, it remains in this state until the amount of free space in the cache exceeds 3.5 TB. The following messages can be displayed on the MI during the limited-free-cache-space-warning state: 

– HYDME0996W 

– HYDME1200W 

For more information, see IBM Knowledge Center. 

Clarification:  Host writes to the disk-only TS7700 cluster and inbound copies continue during this state. 

GLYPH<SM590000> Out of cache resources 

This state occurs when less than 1 TB of free space remains in the cache. After the cache passes this threshold and enters the out-of-cache-resources state, it remains in this state until the amount of free space in the cache exceeds 3.5 TB. 

When a TS7700D cluster is in the out-of-cache-resources state, volumes on that cluster become read-only and one or more out-of-cache-resources messages are displayed on the MI. The following messages can display: 

– HYDME0997W 

– HYDME1133W 

– HYDME1201W 

For more information, see IBM Knowledge Center. 

