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Chapter 3. Requirements and limitations of Red Hat Enterprise Virtualization Hypervisors

This chapter contains all system requirements and limitations which apply to Red Hat Enterprise Virtualization (RHEV) Hypervisors. These requirements are determined by present hardware and software limits as well as testing and support considerations. System requirements and limitations will vary over time due to ongoing software development and hardware improvements.

3.1. System requirements

Red Hat Enterprise Virtualization Hypervisors have the following hardware requirements:
  • A CPU with the hardware virtualization extensions; either an AMD system with AMD-V™ or an Intel system with Intel VT®.
    When the Red Hat Enterprise Virtualization Hypervisor boots a message may appear:
    Virtualization hardware is unavailable.
       (No virtualization hardware was detected on this system)
    This warning indicates the virtualization extensions are either disabled or not present on your processor.


    Some systems have the virtualization extensions disabled in BIOS; virtualization extensions must be enabled in BIOS. First, boot into rescue mode (by typing linux rescue at the RHEV Hypervisor boot prompt) or by entering the shell from the configuration menu. Determine whether your processor has virtualization extensions with this command:
    $ grep -E 'svm|vmx' /proc/cpuinfo
    If any output is shown, the processor is hardware virtualization capable. However in some circumstances manufacturers disable the virtualization extensions in BIOS. As an additional check, verify that the kvm modules are loaded in the kernel:
    # lsmod | grep kvm
    If the output includes kvm_intel or kvm_amd then the kvm hardware virtualization modules are loaded and your system meets requirements.
  • An Intel® 64 or AMD64 CPU extension.
  • At least one network controller with a minimum bandwidth of 1Gbps.
  • At least 512MB of RAM.
  • Sufficient RAM for guest virtual machines. The amount of RAM required for virtual machines depends on:
    • the guest operating system's requirements,
    • the virtual machine's application requirements, and
    • memory activity and usage of the virtual machine.
    KVM can overcommit physical RAM for virtual machines by only allocating RAM for virtual machines as required, and shifting under-utilized virtual machines into swap.
  • The minimum supported internal storage for a Hypervisor is the total of the following list:
    • The root partitions require exactly 512MB of storage.
    • The boot partition requires exactly 50MB of storage.
    • The logging partition is required and the recommended size is 2048MB.
    • The default and minimum size for the configuration partition is 5MB.
    • Swap is required and the recommended size is the recommended swap partition (from this article on Red Hat Knowledgebase) and the overcommit ratio multiplied by the RAM (the default overcommit ratio is 0.5). The minimum size for the swap partition is 5 MB.
      Recommended swap + (RAM * overcommit) = swap partition size
    • The default size of the data partition is the size of the system's RAM plus 512MB. The minimum size is 256MB.

Example 3.1. Determining minimum storage requirements

This example covers the minimum required storage for a RHEV Hypervisor installation on a system with 14GB of RAM (approximately 14,336MB).
The root partitions          = 512MB
The boot partition          = 50MB
The logging partition       = 2048MB
The config partition        = 5MB
The swap partition (using a 0.6 overcommit ratio)
4GB (4096MB) + (0.6 * 14GB) = 12698MB
The data partition is the size of the system's RAM plus 512MB
             (14GB + 512MB) = 14750MB
                      Total = 30063MB
Note, that this is for the minimum storage for an installation. It is recommended to use the defaults, which will use more storage space.