Retain Copy Mode

Retain Copy Mode prevents the copy modes of a virtual volume from being refreshed by an accessing host device if the accessing cluster is not the same cluster that created the volume.

Use the Management Classes panel on the TS7700 Management Interface to enable or disable the Retain Copy Mode. To verify that the Retain Copy Mode is enabled and working, check that the Copy Mode displayed on the Virtual Volume Details page of the management interface remains unchanged following any access of the non-scratch virtual volumes associated with the Management Class in question.

In some grid configurations, virtual volume copies are either not required or intentionally avoided on all clusters. This may be to reduce the replication counts of a volume, or to partition the overall capacity of a grid configuration through selective replication. When these volumes are read or modified through a device on a cluster that did not create the content, the copy modes for the virtual volume can be refreshed, or updated with values from the accessing cluster. The resulting copy modes can be a combination of old and new copy modes, leading to the creation of additional copies not originally requested. When Retain Copy Mode is enabled through the management interface, previously assigned copy modes are retained and subsequent read or modify access does not refresh, update, or merge copy modes. This allows the original number of copies to remain in place.

Note: The Retain Copy Mode option is available only on non-scratch virtual volume mounts.
When enabled for a particular Management Class, Retain Copy Mode ensures that the existing copy mode setting is not changed when any non-scratch virtual volumes that are associated with that Management Class are accessed. Retain Copy Mode does not eliminate existing extra copies, but when enabled prevents extra copies from being made. If copy modes are updated for a given Management Class where Retain Copy Mode is enabled, the new copy modes are only applied to scratch mounts; non-scratch mounts retain the earlier copy mode settings.
Table 1. Effects of Retain Copy Mode in mount scenarios. Table describes scenarios and results for Retain Copy Mode settings.
Scenario Retain Copy Mode setting enabled? Result
Scratch mount is issued Yes Retain Copy Mode setting ignored
Non-scratch mount is issued Yes Grid uses volume's existing copy modes
Non-scratch mount is issued No Grid uses copy modes defined by cluster emulating the device used for the mount
New volume or copy mode not established Yes Grid uses copy modes associated with assigned Management Class
Retain Copy Mode setting is modified on associated Management Classes Yes Management Classes are updated; subsequent copy actions updated only on scratch mounts associated with each Management Class