Virtual machines are all the rage in IT these days -- and rightly so, that's where the future is surely headed. There's less investment in hardware to support them -- than say, their 65# refrigerator-esque predecessors. And they make just dandy web servers (for the most part).

What people fail to see though is that while they appear just like any other server on the network if you RDP to them, that the devil truly is in the details.  VM's usually have about a tenth of the storage of traditional machines and a sliver of RAM over traditional machines and you need to plan for that when you launch a website or a cluster of sites out onto a virtual server.

In the beginning, everything is fine and a great huzzah busts loose that you have now virtualized six of your company's websites on that new Windows 2008 Server with a 20GB hard drive.  That should hold it -- websites are generally pretty small space-wise -- so what's the problem?

The problem is the on-going maintenance involved in running a true "server" engine that's busy cranking out web sessions on a super-lightweight and sparse virtual hardware config. And heaven help you if you're also running your database from that box as well.  (Something, of course, your Blog author would never recommend.)

Windows servers are busy -- very busy logging every little thing that happens to that box. The operating system has multiple logs that are small enough -- but over time, as they begin to collect daily activity, they add to the 'weight' of the machine.  So does IIS and any traffic coming through it.  It all gets logged.  And then there's all that SQL Server database growth, log files and backups, etc.  What's the one thing all of these resources need to keep stable?  They need enough virtualized hard drive space to stash all of these log files and backups.

Problem is, on launch day, the people who deployed the VMs (with 15GB of free disk space) are heroes. But six months from now, just how much content will have been added to those websites?  Is someone with good server knowledge evaluating a Marketing request to drop hundreds of megabytes of video files out into one or more of those websites? 

How many megabytes or gigabytes of log files do you have chewing up that 20GB partition?  That's the problem, and that's where the calls to the help desk usually begin. The website becomes slow -- or God forbid runs out of room -- people complain, and the last thought that usually enters anyone's head is -- does the server have enough room on its virtual drives to do what it needs to do.

So consider this before you take your first plunge in a virtualized web server -- sure, you can run them like a host box, but always remember that they are not a physical box.  Hopefully you have an excellent and versatile SAN device in your configuration -- because keeping your VMs light and clean is important. 

To use a really bad analogy, if a thimble is left outside in a rainstorm, it's going to fill up quicker than a large bucket.  So if your enterprise has lots of thimbles in the rainstorm -- just make sure some one is keeping an eye on their system resources -- and above all -- make sure those machines are attached to a SAN and on good backup plans.