CentOS 5 Virtualization Guide - Chapter 1. System requirements

Chapter 1. System requirements

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This chapter lists system requirements for successfully running virtualization on Red Hat Enterprise Linux. You require a system running Red Hat Enterprise Linux 5 Server with the virtualization packages. The host needs a configured hypervisor . For information on installing the hypervisor, read Chapter 4, Installing Red Hat Virtualization packages on the host .

Minimum system requirements

6GB free disk space
2GB of RAM.

Recommended system requirements

6GB plus the required disk space recommended by the guest operating system per guest. For most operating system guests greater than 6GB is recommended.
One processing core or hyper-thread for each guest and one for the hypervisor.
2GB of RAM plus the recommended RAM required by the guest operating system for each guest.

You want to virtualize three guests running application XYZ on Red Hat Enterprise Linux. Red Hat Enterprise Linux 5 requires 5GB of disk space and application XYZ requires 2GB of disk space. Red Hat Enterprise Linux requires a minimum of 512MB of RAM application XYZ requires up to 256MB of RAM. Application XYZ runs best on just one processing core.

The minimum system requirements for a system running application XYZ on three Red Hat Enterprise Linux guests are:

21GB of free disk space available to the host,

2304MB(768GB x 3) + 1024MB(for the host) = approximately 3.5GB of RAM, and

3 processing cores + 1 for the host(for better performance).

Example 1.1. Requirements for a hypothetical virtualization system

There are additional requirements for para-virtualization and full virtualization.

Para-virtualization requirements

Para-virtualized guests require the Red Hat Enterprise Linux 5 installation tree available over NFS, FTP or HTTP.

Full virtualization requirements

Full virtualization requires DVD, CD-ROM or bootable .iso file installation media.

Full virtualization requires CPUs with hardware virtualization extensions. This section describes how to identify hardware virtualization extensions and enable them in your BIOS if they are disabled. If hardware virtualization extensions are not present you can only use para-virtualization with Red Hat Virtualization.

The virtualization extensions can not be disabled in the BIOS for AMD-V capable processors installed in a Rev 2 socket. The Intel® VT extensions can be disabled in the BIOS. Certain laptop vendors have disabled the Intel® VT extensions by default in their CPUs.

These instructions verify whether the Intel® VT virtualization extensions are enabled or if the instructions are disabled in BIOS:

Run the xm dmesg | grep VMX command. The output should display as follows:
```
(XEN) VMXON is done
(XEN) VMXON is done
```

Run the cat /proc/cpuinfo | grep vmx command to verify the CPU flags have been set. The output should be similar to the following. Note vmx in the output:

flags   : fpu tsc msr pae mce cx8 apic mtrr mca cmov pat pse36 clflush 
dts acpi mmx fxsr sse sse2 ss ht  tm syscall lm constant_tsc pni monitor ds_cpl
vmx est tm2 cx16 xtpr lahf_lm

Do not proceed if the output of xm dmesg | grep VMX is not VMXON is done for each CPU. Please visit the BIOS if other messages are reported.

The following commands verify that the virtualization extensions are enabled on AMD-V architectures:

Run the xm dmesg | grep SVM command. The output should look like the following:

(XEN) AMD SVM Extension is enabled for cpu 0
(XEN) AMD SVM Extension is enabled for cpu 1

Run the cat /proc/cpuinfo | grep svm to verify the CPU flags have been set. The output should be similar to the following. Note svm in the output:

flags   :  fpu tsc msr pae mce cx8 apic mtrr mca cmov pat pse36 clflush
mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt lm 3dnowext 3dnow pni cx16
lahf_lm cmp_legacy svm cr8legacy ts fid vid ttp tm stc

The virtualization extensions are sometimes disabled in BIOS, usually by laptop manufacturers. Refer to Section 28.12, “Enabling Intel VT and AMD-V virtualization hardware extensions in BIOS” for instructions on enabling disabled virtualization extensions.

Storage support

The supported guest storage methods are:

files on local storage,
physical disk partitions,
locally connected physical LUNs,
LVM partitions, and
iSCSI and Fibre Channel based LUNs.

File based guest storage

File based guest images should be stored in the /var/lib/xen/images/ folder. If you use a different directory you must add the directory to your SELinux policy. For more information see Section 10.1, “SELinux and virtualization”.