Any rack will do as it only requires two posts. It doesn't require a 4 post rail system. However, the VSP 9000 is extremely deep so if you plan on getting an enclosed rack make sure it's deep enough.
Also, make sure you buy a proper data comm rack. Seen too many people use server racks for switches and it never ends well.
• Height: 61.91cm (24.375in.) or 14RU
• Width: 44.45cm (17.5in.)
• Depth: 82.55cm (32.5in.)
• Weight (empty): 73kg (160lb)
• Weight (fully loaded): 131kg (288lb)