Chapter 2. Requirements

2.1. Hypervisor Requirements
2.2. Guest Requirements and Support Limits
2.3. Guest Operating System Support

This chapter contains all system requirements and limitations which apply to Red Hat Enterprise Virtualization Hypervisors. These requirements are determined based on 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.

2.1. Hypervisor Requirements

Red Hat Enterprise Virtualization Hypervisors have a number of hardware requirements and supported limits.

Table 2.1. Red Hat Enterprise Virtualization Hypervisor Requirements and Supported Limits

Item	Support Limit
CPU	A minimum of 1 physical CPU is required. All CPUs must support: the Intel® 64 or AMD64 CPU extensions, and the AMD-V™ or Intel VT® hardware virtualization extensions. A maximum of 128 physical CPUs is supported.
RAM	A minimum of 512 MB of RAM is required. A minimum of an additional 512 MB for each virtual machine is recommended. The amount of RAM required for each guest varies depending on: the guest operating system's requirements, the guests' application requirements, and memory activity and usage of guests. Additionally KVM is able to over-commit physical RAM for virtualized guests. It does this by only allocating RAM for guests as required and shifting underutilized guests into swap. A maximum of 1 TB of RAM is supported.
Storage	The minimum supported internal storage for a Hypervisor is the total of the following list: The root partitions require at least 512 MB of storage. The configuration partition requires at least 8 MB of storage. The recommended minimum size of the logging partition is 2048 MB. The data partition requires at least 256 MB of storage. Use of a smaller data partition may prevent future upgrades of the Hypervisor from the Red Hat Enterprise Virtualization Manager. By default all disk space remaining after allocation of swap space will be allocated to the data partition. The swap partition requires at least 8 MB of storage. The recommended size of the swap partition varies depending on both the system the Hypervisor is being installed upon and the anticipated level of overcommit for the environment. Overcommit allows the Red Hat Enterprise Virtualization environment to present more RAM to guests than is actually physically present. The default overcommit ratio is `0.5`. The recommended size of the swap partition can be determined by: Multiplying the amount of system RAM by the expected overcommit ratio, and adding 2 GB of swap space for systems with 4 GB of RAM or less, or 4 GB of swap space for systems with between 4 GB and 16 GB of RAM, or 8 GB of swap space for systems with between 16 GB and 64 GB of RAM, or 16 GB of swap space for systems with between 64 GB and 256 GB of RAM. Example 2.1. Calculating Swap Partition Size For a system with 8 GB of RAM this means the formula for determining the amount of swap space to allocate is: (8 GB x 0.5) + 4 GB = 8 GB Please note that these are the minimum storage requirements for Hypervisor installation. It is recommended to use the default allocations which use more storage space.
PCI Devices	At least one network controller is required with a recommended minimum bandwidth of 1 Gbps.

Important — Virtualization Extensions

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. Ensure that the CPU supports the listed extensions and they are enabled in the system BIOS.

To check that processor has virtualization extensions, and that they are enabled:

At the Hypervisor boot screen press any key and select the Boot or Boot with serial console entry from the list. Press Tab to edit the kernel parameters for the selected option. After the last kernel parameter listed ensure there is a Space and append the rescue parameter.
Press Enter to boot into rescue mode.
At the prompt which appears, determine that your processor has the virtualization extensions and that they are enabled by running this command:
```
# grep -E 'svm|vmx' /proc/cpuinfo
```
If any output is shown, the processor is hardware virtualization capable. If no output is shown it is still possible that your processor supports hardware virtualization. In some circumstances manufacturers disable the virtualization extensions in the BIOS. Where you believe this to be the case consult the system's BIOS and the motherboard manual provided by the manufacturer.
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.

Important — `Fakeraid Devices` are not Supported

The Red Hat Enterprise Virtualization Hypervisor does not support installation on fakeraid devices. Where a fakeraid device is present it must be reconfigured such that it no longer runs in RAID mode.

Access the RAID controller's BIOS and remove all logical drives from it.
Change controller mode to be non-RAID. This may be referred to as compatibility or JBOD mode.

Access the manufacturer provided documentation for further information related to the specific device in use.