HP is so confident its 3PAR storage arrays will double a server's virtual machine count that it's guaranteeing it - and will pay for any extra 3PAR storage needed beyond what it replaces to get to the 2x VM count number.
The HP Get Virtual Guarantee Program states uncompromisingly:
Clients deploying HP 3PAR systems with VMware vSphere version 4.1 or later are guaranteed a 2x increase in virtual machine density on physical servers in comparison to their VM density with previously installed storage … If a two times increase in virtual server density is not achieved, HP will provide participants with the disk capacity and related HP software and support necessary to achieve the guaranteed program results.
The HP Get Virtual Guarantee Program is available to clients globally through HP and HP-authorized channel partners.
HP specifies: "To participate in the program, qualified participants must purchase an HP 3PAR Storage System with HP 3PAR Optimization Suite Software for autonomic load balancing and HP 3PAR System Reporter Software. Clients also must be running VMware vSphere version 4.1 or higher." ®