Hitachi VSP G1000 User Manual page 24

see Creating Thin Image pairs using Device Manager - Storage Navigator on
page 130.
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.
24 Overview of Thin Image
Hitachi Thin Image User Guide for Hitachi Virtual Storage Platform G Series and F Series