Essentially, one RVU is equivalent to one activated processor core of a host within the virtualization infrastructure being managed by BigFix. This is one-to-one until you reach 2500, when discounts for higher quantities kick in. This licensing metric will cover as many VMs as your infrastructure supports.
Another approach is to buy Managed Virtual Servers (MVS) licenses, where each VM and physical server is counted as one MVS. Which approach you take depends on the density of virtualization.
The language from the BigFix Platform License Document:
The following units of measure may apply to Licensee’s use of the Program.
Client Device is a unit of measure by which the Program can be licensed. A Client Device is a single user computing device or special purpose sensor or telemetry device that requests the execution of or receives for execution a set of commands, procedures, or applications from or provides data to another computer system that is typically referred to as a server or is otherwise managed by the server. Multiple Client Devices may share access to a common server. A Client Device may have some processing capability or be programmable to allow a user to do work. Examples include, but are not limited to actuators, appliances, automated teller machines, automatic meter readers, cash registers, disk drives, desktop computers, kiosks, notebook computers, personal digital assistant, point-of-sale terminals, sensors, smart meters, tape drives, and technical workstations. Licensee must obtain entitlements for every Client Device which runs, provides data to, uses services provided by, or otherwise accesses the Program and for every other computer or server on which the Program is installed.
Managed Virtual Server
Managed Virtual Server is a unit of measure by which the Program can be licensed. A server is a physical computer that is comprised of processing units, memory, and input/output capabilities and that executes requested procedures, commands, or applications for one or more users or client devices. Where racks, blade enclosures, or other similar equipment is being employed, each separable physical device (for example, a blade or a rack-mounted device) that has the required components is considered itself a separate server. A virtual server is either a virtual computer created by partitioning the resources available to a physical server or an unpartitioned physical server. Licensee must obtain Managed Virtual Server entitlements for each virtual server managed by the Program.
Resource Value Unit (RVU)
Resource Value Unit (RVU) is a unit of measure by which the Program can be licensed. RVU Proofs of Entitlement are based on the number of units of a specific resource used or managed by the Program. Licensee must obtain sufficient entitlements for the number of RVUs required for Licensee’s environment for the specific resources as specified in the table below. RVU entitlements are specific to the Program and the type of resource and may not be exchanged, interchanged, or aggregated with RVU entitlements of another program or resource.
Instead of the entitlements required for the Resources used by the Program directly, Licensee must obtain entitlements for this Program sufficient to cover the Resources managed by the Program.
In addition to the above, the following terms apply to Licensee’s use of the Program.
The Resources for the purpose of the RVU calculation are Activated Processor Cores managed by the Program. An Activated Processor Core is a processor core that is available for use in a physical or virtual server, regardless of whether the capacity of the processor core can be or is limited through virtualization technologies, operating system commands, BIOS settings, or similar restrictions. Licensee can deploy the Program using either Full Capacity licensing or Virtualization Capacity (Sub-Capacity) licensing according to the Passport Advantage Sub-Capacity Licensing Terms (see webpage below). If using Full Capacity licensing, each Activated Processor Core in the physical hardware environment managed by the Program must be counted, except for those servers from which the Program permanently no longer manages. If using Virtualization Capacity licensing, the Virtualization Capacity License Counting Rules at http://www.ibm.com/software/lotus/passportadvantage/Counting_Software_licenses_using_specific_virtualization_technologies.html defines how many Activated Processor Cores must be counted.
From 1 to 2,500 Resources, 1.0 RVU per Resource
From 2,501 to 10,000 Resources, 2,500 RVUs plus 0.8 RVUs per Resource above 2,500
From 10,001 to 50,000 Resources, 8,500 RVUs plus 0.6 RVUs per Resource above 10,000
From 50,001 to 150,000 Resources, 32,500 RVUs plus 0.4 RVUs per Resource above 50,000
For more than 150,000 Resources, 72,500 RVUs plus 0.2 RVUs per Resource above 150,000