Cascaded pairs are volume pairs created in the first and second layer. A pair made up of an L1 S-VOL and a layer-2 (L2) S-VOL is an L2 pair. You can pair each SI L1 S-VOL with two L2 S-VOLs. You can pair nine L1 and L2 S-VOLs with a P-VOL.
The following image shows the structure of cascaded pairs.
In cascaded pairs, the P-VOL for an L1 pair is a root volume and the S-VOL is a node volume. The P-VOL for an L2 pair is the S-VOL of an L1 pair, a node volume, and the S-VOL is a leaf volume.