It seems to me that there is still a large amount of confusion concerning virtualisation in general and VMware specifically. The problem stems from the fact that most users of virtualisation don’t understand the real benefits ( and pitfalls ) of this interesting technology – I’ll attempt to provide some insight here.
Benefits
- Make better use of hardware resulting in better efficiencies – instead of having machines idling for most of the time running only one application, get them to work harder on average loads by having them run multiple applications ( which are still partitioned by the separate VMs )
- Easily bring new machines online either via a normal install or VM imaging
- Centralise install images using ISO files
- Run more applications than you would normally have hardware for
- Some virtualisation solutions have the ability to move a VM from one physical hardware platform to another while the VM is online ( hot migration ) – this allows you to take hardware in and out of service without affecting your applications ( for VMware this requires VirtualCentre with VMotion )
- Most virtualisation solutions have a VM snapshot capability which provides a point-in-time backup ability
- Virtualisation can bring some power savings to computing data centres as less physical hardware is typically used and the average load of power supplies is increased resulting in better power efficiencies
Disadvantages
- Reliability of the host server becomes much more important as it’s no longer running just one system, but multiple
- The ease of installing new VMs can result in overloading or mismatching of VM logical hardware
- Due to requiring iSCSI or SAN-based storage for the central VM store, setting up virtualisation can initially be much more complex
And finally, some tips and tricks
- If you are going to use iSCSI, make sure you setup a service console for the Ethernet card(s) being used for the iSCSI connection, otherwise you won’t be able to see anything ( if you are using VMWare ESX )
- While iSCSI is fine for low end use, you should really be using an FC-based storage subsystem for the central VMFS store
- Various virtualisation solutions have different architectures, eg. paravirtualisation, emulation, hardware level virtualisation – make sure you understand what you require and what you are getting
