Virtualize multiple servers on single box or not?

Question

Hey all...Forgive me, as I am not up to speed on my server administration abilities. I'm currently looking at specifications for a new server that I need to build. The server will need to serve multiple duties such as:

• web server
• hosting SQL Server 2008
• possible development staging server

I am planning on installing Windows Server 2008, but was needing to know whether it would be more efficient to install multiple independent virtual servers on the same box; one for the web server, one for the database server, etc, or to just install Windows Server and SQL Server on the same OS instance. What are the advantages and disadvantages of these approaches, and at what point would I need to consider moving to a multi-server architecture.

I understand that the performance has a lot to do with it, so for the sake of discussion, lets say the server will have Dual-QC Xeon (approx. 2.66 GHz) and 16-32 GB (memory is just too cheap). Thanks.

Answer 1

One of the main advantages you get from virtualisation is that your 3 components are now independant, your developers can mess with the staging server, break it, without affecting the SQL or web server. If you find you need to reboot one server, you can do so without affecting the others.

It also means you can split resources, if your web server uses alot of memory you can give it some extra and take some away from the development server, without worrying that teh developers will run some memory intensive app that will stop your web applications running.

It also makes backups easier, you can take an image of a whole machine, and easily restore it if a problem occurs, even to new hardware.

There are however some downsides, resource use will be more, your running 3 OS's instead of 1 (or 4 if you count the host), that's 3 extra kernels needing memory and CPU power, and disk space. There's also the extra cost of licensing, both in terms of windows licence as and CALs.

Answer 2

Seperate VMs give you the option to move to independent physical hardware later on with much less pain. Using modern virtualization products and choosing a total number of cores across all your VMs that is less than your total (8) will help.

For instance, if you give your Production Web Server VM 2 cores, Production SQL VM 2 cores, Development Web Server 1 core, and Development SQL VM 1 core, you should be fine.

Another key thing that will help is getting fast disks, and isolating machines to seperate disks, or going with some heavy duty solution like a SAN. We use a SAN at work to feed 30 different VMs running on a blade farm and it works incredibly well. It's just expensive.

Answer 3

CPU won't likely be a factor but IO will be. If you don't knwo the workload be prepared to upgrade the disks to a faster array(which are not mentioned). I would start off with at least a dual port nic added to whatever you currently have (I am banking on at least 1 other nic already there). This will allow you to put the webservers in a DMZ and keep the rest of the servers behind the firewall. (you could use vlan tags but I'n not a huge fan of them)

Answer 4

Not unless you have backup hardware handy and ready to be deployed on a moment's notice. Single points of failure are what in the industry call "Bad Things".