Image mode space-efficient VDisks

When you create an image mode virtual disk (VDisk), you can designate it as space-efficient. An image mode space-efficient VDisk has a virtual capacity and a real capacity.

An image mode space-efficient VDisk has a direct relationship with a single MDisk where the contents of the MDisk map to the real capacity that is used by the space-efficient VDisk. Unlike fully-allocated VDisks, the logical block address (LBA) on the MDisk is not necessarily the same as the LBA on the VDisk. You cannot change the real capacity of an image mode space-efficient VDisk, manually or by using the autoexpand feature. To use the autoexpand feature, the VDisk must be in managed mode.

You can use an image mode VDisk to move a space-efficient VDisk between two SAN Volume Controller clusters using the following procedure. The procedure is similar to that used for fully-allocated VDisks, but has an extra step during the import process to specify the existing space-efficient metadata, rather than to create a new, empty VDisk.

If the VDisk is not already in image mode, migrate the VDisk to image mode and wait for the migration to complete.
Delete the VDisk from the exporting cluster.
Disconnect the MDisk from the exporting cluster and connect the MDisk to the importing cluster.
Create a new image mode space-efficient VDisk using the MDisk. You must specify the import option.
Optionally, migrate the VDisk to managed mode.

The import option is only valid for SAN Volume Controller space-efficient VDisks. If you use this method to import a space-efficient volume that is created by RAID controllers into a cluster, SAN Volume Controller cannot detect it as a space-efficient VDisk. However, you can use the VDisk mirroring feature to convert an image-mode fully allocated VDisk to a space-efficient VDisk.