Everything About [Computers :: Virtualization]

Benefits

Consolidation is only one aspect of virtualizing PC's, there's a good many other benefits from having this abstraction layer (such as security, redundancy, portability, electric bills, licensing, etc)

Microsoft vs VMware

Microsoft has historically not paid much development resources to virtualization, but that's not necessarily to say they're behind the curve either (even though they are at the moment). They did what all big companies do, buy the technology... Virtual PC 2004 is actually Connectix Virtual Server made free after the aquisition. Virtual PC 2007 only solidified and expanded it's current ability. Windows Server 2008 has virtualization built in... and attempts to leapfrog back into the competitive fray (overnight as it were). The market implications alone of having this ability in every Windows server is compelling.

VMware for Dummies:
Server = Can create & run virtual machines
Player = Can only run virtual machines, not create

Storage

A virtual disk is simply a file (e.g. test_box.vmdk) you can store on any medium (local drive, network drive, removable drive). It would be the equivalent of zip'ing up your entire hard drive into a single file. With virtual drives, you can either a.) have them grown & shrink as you create & delete files on the virtual disk, or b.) allocate an entire amount from the get-go. For reasons I won't go into, you should almost always use the grow/shrink method. Benefits of a virtual disk include being able to literally copy the virtual machine (vm) to another computer, and launching the virtual machine on completely different hardware... all without the vm knowing. Also, where storage space is a limitation, it's also a better consolidation.

A physical disk is quite literally giving the vm direct access to a very real, physical disk. My Xample before was, that you can put the vm's OS installation on a virtual drive (c:) and add a physical partition (d:) where you might want to save all your music/videos/etc. Advantage is, other vm's and host operating system can also directly share the same partition/drive, just as if it were it's own. The side effect being, that if multiple machines think it's under their sole ownership, and try to all change files all at the same time.

In VMware, you can use either preallocated virtual disks or growing volumes, with the primary differences being higher performance with preallocated and space savings with growing volumes. However, one of the limitations of preallocated disks is you may not grow or shrink them (think PowerQuest). The prescribed way to enlarge a preallocated partition is to back it up using conventional means (Ghost, etc) and restore an image on a larger virtual disk.

Snapshots

VMware has the ability to take a Snapshot of a system, to where if something happens to the system... you can quickly revert all your changes to that snapshot. Okay, that's great... but now there's something very important that you should know.

If you have a Virtual Machine with a 15GB Partition, and you take a snapshot... the 15GB partition is essentailly frozen on the Host Machine. Any and all changes are then created in a completely new file (or set of files). The way snapshots work is, you can either commit those changes by essentially overwriting the original 15GB of files, or you can revert to the snapshot by deleting all those new files.

!! Beware / Caution !!

You will get a very nasty message in the Virtual Machine saying the Host OS has run out of disk space and if you don't do something, the Virtual Machine will corrupt itself (loose everything). The previously mentioned virtual machine with a measily 15GB Virtual Machine is now taking TWICE that in storage! The fix: remove the snapshot (which saves all changes).

Just imagine in a production system if this happened with many virtual machines on the same PC, all with their own archives of snapshots.... wphew, that can really catch a System Administrator offguard with immediately fleeting storage capacity!