When a storage device whose firmware version is V11L10-2000 or later is used, backup operations are available where snap generations are managed by deleting a specific snap generation other than the oldest among the multiple snap generations created with SnapOPC+. Note that when SnapOPC+ is used in a backup operation environment that meets all the following conditions, the required number of free volumes must be configured as described in this section.
When the copy source volume of SnapOPC+ is in a storage device whose firmware version is V11L10-2000 or later
When multiple copy groups are created for the above copy source volume
When management of the snap generation for the copy source volume is performed automatically with the acsnap start command
When multiple copy groups are defined for one copy source volume and a backup operation is performed with SnapOPC+, the generation number of the oldest snap generation may not be "1" in the target copy groups.
For example, when two copy groups (copy group A and copy group B) are defined with five copy pairs, if five snap generations are created for copy group A and after that five snap generations are created for copy group B, the generation number of the oldest snap generation for copy group B is "6".
The acsnap start command attempts to delete the oldest snap generation for the specified copy group and to retrieve the latest snap generation. When the acsnap start command is executed on a copy group where the generation number of the oldest snap generation is not "1", the data of the deletion target snap generation is migrated to the snap generation prior to it, so the snap generation deletion process may take some time. If the snap generation deletion process is not completed and a free volume does not exist in the copy group, the acsnap start command terminates with an error because the latest snap generation cannot be retrieved.
Even if the snap generation deletion process is not completed, the latest snap generation can be retrieved if one or more free volumes exist in the copy group. To retrieve the latest snap generation even if the snap generation deletion process is not completed, at least one free volume is required in the copy group. This can be set with "setting the required number of free volumes".
Refer to the example in "2.6.1 Automatic Management of Snap Generations" and set the required number of free volumes, as necessary.
