Hitachi G1000 User Manual page 45

You can create up to three ShadowImage pairs respectively on the GAD
primary and secondary systems.
Because the server recognizes a GAD pair as one volume, it sees the volume
as paired with six ShadowImage volumes.
You can create three additional, cascaded SI pairs using the SI S-VOLs. This
means that up to nine SI pairs can be created with the GAD P-VOL, and nine
SI pairs can be created with the GAD S-VOL.
2-7
System requirements
Hitachi Virtual Storage Platform G1000 Global-Active Device User Guide