However, if GM operations experience degraded response times from the secondary system for an extended period, I/O operations begin to queue at the primary system. This queue results in an extended response time to application hosts. In this situation, the gmlinktolerance  feature stops GM relationships, and the application host’s response time returns to normal. 

After a 1920  event occurs, the GM auxiliary volumes are no longer in the consistent_synchronized  state until you fix the cause of the event and restart your GM relationships. For this reason, ensure that you monitor the system to track when these 1920 events occur. 

You can disable the gmlinktolerance  feature by setting the gmlinktolerance  value to zero. However, the gmlinktolerance  feature cannot protect applications from extended response times if it is disabled. It might be appropriate to disable the gmlinktolerance  feature under the following circumstances: 

GLYPH<SM590000> During SAN maintenance windows in which degraded performance is expected from SAN components, and application hosts can withstand extended response times from GM volumes. 

GLYPH<SM590000> During periods when application hosts can tolerate extended response times and it is expected that the gmlinktolerance  feature might stop the GM relationships. For example, if you test by using an I/O generator that is configured to stress the back-end storage, the gmlinktolerance  feature might detect the high latency and stop the GM relationships. Disabling the gmlinktolerance  feature prevents this result at the risk of exposing the test host to extended response times. 

A 1920  event indicates that one or more of the SAN components cannot provide the performance that is required by the application hosts. This situation can be temporary (for example, a result of a maintenance activity) or permanent (for example, a result of a hardware failure or an unexpected host I/O workload). 

If 1920  events are occurring, it can be necessary to use a performance monitoring and analysis tool, such as the IBM Virtual Storage Center, to help identify and resolve the problem. 

## 10.9.4 System partnership 

To create an IBM SAN Volume Controller or an IBM Storwize system partnership, use the mkfcpartnership  command for traditional Fibre Channel (FC or FCoE) connections or mkippartnership  for IP-based connections. 

## The svctask mkfcpartnership command 

Use the mkfcpartnership  command to establish a one-way MM/GM partnership between the local system and a remote system. Alternatively, use mkippartnership  to create IP-based partnership. 

To establish a fully functional MM/GM partnership, you must issue this command on both systems. This step is a prerequisite for creating MM/GM relationships between volumes on the IBM Spectrum Virtualize systems. 

When the partnership is created, you can specify the bandwidth to be used by the background copy process between the local and remote system. If it is not specified, the bandwidth default is 50 MBps. The bandwidth must be set to a value that is less than or equal to the bandwidth that can be sustained by the intercluster link. 

