Creating cascaded pairs
Thin Image S-VOLs can be paired with secondary layer S-VOLs. First layer (L1) S-VOLs can also be paired with secondary layer (L2) S-VOLs. A maximum of 64 layers can be created, and a maximum of 1,024 S-VOLs can be used for a P-VOL. In this case, the snapshot tree is cascaded.
L2 to L64 pairs are called cascaded pairs. The following figure illustrates the configuration of cascaded snapshot trees.
- The volume in the top layer of the snapshot tree (P-VOL of the L1 pair) is the root volume.
- Volumes between the root and leaf volumes are node volumes.
- Volumes in the bottom layer of the snapshot tree are leaf volumes.
To create a Thin Image pair that can be used in a cascaded snapshot tree, open the Create TI Pairs window and select Enable for Cascade. For details, see Creating Thin Image pairs using Device Manager - Storage Navigator.
When the S-VOL of a Thin Image pair you created for a P-VOL for the first time is a DP-VOL, you can create cascaded pairs. If a Thin Image pair whose secondary volume is a Thin Image V-VOL (which has the Snapshot provisioning type) is created, remove the pair first, and then create another Thin Image pair whose secondary volume is a DP-VOL.
A snapshot tree can be configured by combining snapshot and cloned pairs. As shown in the following figure, you can also cascade pairs that are being cloned, but you can only clone up to three pairs concurrently. The following figure shows an example of when pairs that are being cloned are also cascaded.
You can use the S-VOL of a cascaded and cloned pair as a new L1 pair of the P-VOL. In this case, the volume is the root volume, and a node or leaf volume.