Over the last few weeks, I have looked at the various pros

and cons of virtualisation—the benefits it may offer considered next to the

risks it can pose. Overall, I am of the opinion that in most circumstances where

hardware utilisation is minimal, the advantages of virtualisation far outweigh

any added risk (which can be counteracted by introducing high-availability

safeguards).

Once you’ve decided that virtualisation is suitable in your

circumstances, consideration must be given as to which particular offering will

be the best fit. The first consideration is that of Para-, OS, or Hardware

virtualisation—the differences described in my previous


blog. I personally favour hardware virtualisation, as it has many relative

strengths. First, the systems become hardware-independent, which means

recovering a server farm to a slightly different hardware base should be no

issue; hardware upgrades should cause little in the way of problems; and most

importantly, should one virtual machine crash, the total separation of machines

means that others on the same host will be unaffected. Another positive trait

of hardware virtualisation is that it gives you the ability to run various

different operating systems on one host (so you can have Windows, Linux, and

BSD virtual machines running on one physical server) without requiring any modification

of the guest system. Obviously, I am biased in that I am looking at this from

the point of view of a sys admin who manages an environment containing an

assortment of different operating systems—sys admins working for a web hosting

firm, where each machine is the same, may well favour another method.

I would say that the three major hardware virtualisation

platforms are Virtual Server 2005 R2, VMware Server, and VMware ESX server. Virtual

Server 2005 R2 will only run on a Microsoft Windows host; VMware Server will

run on both Windows and Linux hosts (I have tried both); whereas, VMware ESX

server installs to ‘Bare Metal.’ Let’s take a look at the feature sets and

claimed benefits of each offering:

Virtual Server 2005
R2:

  • It’s
    free!
  • Runs

    most major 32bit x86 operating systems in the virtual machine guest

    environment

  • iSCSI
    clustering for guests to guest across physical machines
  • Add-ins

    provide even greater CPU and IO performance for Windows Server guest

    operating systems and certain third-party x86 operating systems

VMware Server:

  • It’s
    also free!
  • Supports
    64-bit guest operating systems
  • Supports
    two-processor Virtual SMP for guest machines
  • Runs
    on Windows or Linux host
  • Opens

    VMware or Microsoft virtual machine format and Symantec LiveState Recovery

    images with VM Importer

  • Protects
    investment with an easy upgrade path to VMware Infrastructure

VMware ESX server:

  • Install
    to ‘Bare Metal’–no host Operating System
  • RAM

    over-commitment: Safely allocate 16GB of virtual memory with only 8 GB of

    physical memory

  • Transparent

    page sharing: Utilize available memory more efficiently by storing memory

    pages identically across multiple virtual machines only once

  • 4-Way
    Virtual SMP
  • Support

    for powerful physical server systems: Up to 32 logical CPUs and 64 GB RAM

    for large-scale server consolidation

It’s pretty obvious that Virtual Server 2005 R2 and VMware Server

are in direct competition—they are both free (Microsoft doing this as they gain

on the use of virtual machines in licensing terms; VMware doing this to

directly compete). VMware ESX server is a high-end system aimed at serious

large-scale consolidation projects and attempts to make virtualisation a

realistic platform for even the most demanding database and number-crunching

operations. The best way to find out which system is best for your own

circumstance is to try both—Virtual Server 2005 R2 can be downloaded here


for free and VMware Server can be found here. I personally prefer

VMware; not simply because “it isn’t Microsoft,” but because:

a) I

have used VMware Workstation on/off for years and find the interface very

intuitive and the operation of VMware Server to be almost identical.

b) Running

on a Linux host, in my opinion, has performance advantages and also means your

host machine can be licence-free (Ubuntu is one of the recommended host

systems).

c) The

disk image format is standardised and its ability to import virtual machines

from other platforms eases any migration.

These are, of course, only three of many virtualisation

solutions on the market; others which I think deserve a mention would be Xen,

Linux V-Server, and Virtuozzo. A side by side comparison of most virtualisation

products can be found here in Wikipedia

placed in an easy-to read-table. This includes links to the relative websites,

details of the supported guest/host environments, and an indication as to their

performance—I would highly recommend you check it out.