Virtualization limits for Red Hat Enterprise Linux hypervisors

a) Red Hat® Enterprise Linux® 5 KVM and Xen Virtualization
b) Red Hat Enterprise Linux 6 KVM Virtualization
c) Red Hat Enterprise Virtualization Hypervisor

Also see Red Hat Enterprise Linux technology capabilities and limits (supported[/theoretical])1

  RHEL 5 XEN x86 RHEL 5 XEN x64 RHEL 5 KVM RHEL 6 KVM
Maximum number of cores in host
  322 160 160 160 / 4096
Maximum memory in host
  N/A N/A 1TB 2TB / 64TB
Maximum number of virtual CPUs in paravirtualized guest
x86 322 322 N/A N/A
x86_64 N/A 322 N/A N/A
Maximum memory in paravirtualized guest (x86)
x86 64GB 64GB N/A N/A
x86_64 N/A 168GB N/A N/A
Maximum number of virtual CPUs in fully virtualized guest
x86 322 322 16 160
x86_64 N/A 322 16 160
Maximum memory in fully virtualized guest
x86 8GB 64GB 512GB3 2TB3
x86_64 N/A 512GB4 512GB4 2TB4
Minimum memory in fully virtualized guest
x86 512MB 512MB 512MB 512MB
x86_64 512MB 512MB 512MB 512MB5

Notes:

  1. Supported limits reflect the current state of system testing by Red Hat and its partners for mainstream hardware. Systems exceeding these supported limits may be included in the Hardware Catalog after joint testing between Red Hat and its partners. If they exceed the supported limits posted here, entries in the Hardware Catalog will include a reference to the details of the system-specific limits and are fully supported. In addition to supported limits reflecting hardware capability, there may be additional limits under the Red Hat Enterprise Linux subscription terms. Supported limits are subject to change as ongoing testing completes.
  2. Supports a maximum of 125 CPUs across entire machine.
  3. KVM does support the maximum supported memory and it can be allocated to the guest. However, 32-bit guest with Physical Address Extension (PAE) support will show 64GB. This is a hardware limitation, not a KVM limitation.
  4. Requires Intel EPT or AMD RVI technology support.
  5. This is the recommended limit in text mode, and graphical mode requires 1GB.