V-VOLs are virtual volumes that do not have any physical storage space.
Thin Image uses Thin Image V-VOLs (V-VOLs of provisioning type Snapshot in HDvM - SN, or V-VOLs created by the raidcom add ldev -pool snap command in CCI) or DP-VOL as V-VOLs. Thin Image V-VOLs and DP-VOLs are referred to as virtual volumes (V-VOLs) in this document. Use DP-VOLs to create cascaded or cloned pairs. Use Thin Image V-VOLs to create snapshot pairs. Note that you can use DP-VOLs to cascade snapshot pairs.
Thin Image uses V-VOLs to access snapshot data from hosts or clone pairs, so if you create clone pairs or use snapshot pairs (a pair with the snapshot attribute) to access snapshot data from hosts, then V-VOLs are required to create Thin Image pairs or assign an S-VOL to snapshot data. If the storage system or snapshot pair does not need to access snapshot data from hosts, V-VOLs are not necessary.
You can release the V-VOLs that are being used as Thin Image S-VOLs from assignment of snapshot data. Released V-VOLs can be assigned to other snapshot data. However, you cannot release allocation of V-VOLs used as node volumes to snapshot data or allocate the V-VOL to different snapshot data. Also, you cannot release allocation of V-VOLs which are being used for the S-VOL of a clone pair to snapshot data, or allocate it to different snapshot data.
If you release a V-VOL being used as a Thin Image S-VOL from assignment to snapshot data, and then assign the V-VOL to different snapshot data, this V-VOL becomes the S-VOL of another pair. Therefore, each time you assign a V-VOL to snapshot data, execute the command which allows the host server to recognize the device.
You cannot release definitions of V-VOLs if the V-VOLs are being used as Thin Image secondary volumes; you must first release the Thin Image pairs that are using the V-VOLs.