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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.

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4 Answers

up vote 2 down vote accepted

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.

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Windows licensing depends on what OS you get and if you get datacenter (which is $50 more than enterprise) you get unlimited VMs. There is a cost calculator at microsoft.com/windowsserver2008/en/us/hyperv-calculators.aspx –  Jim B Jul 9 '09 at 18:52
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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.

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Bob, when you are referring to "fast" disks, what speed would you consider appropriate? Is 7200 too slow, maybe a 10k RPM or 15k RPM? –  user12288 Jul 9 '09 at 16:38
    
As fast as you can afford is the glib answer. 10K disks make the world of difference over 7200. 15K are even more noticeable. –  Bob King Jul 9 '09 at 18:06
    
I completely disagree- I'll take 10 7200 disks over 3 15k disks every day of the week and crush the 15k disks performancewise. You don't need "fast" disks you need fast I/O –  Jim B Jul 9 '09 at 18:46
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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)

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I plan on doing a server colocation and renting out rackspace, so I'm not sure if the network will be much of an issue. –  user12288 Jul 9 '09 at 16:33
    
You still want multiple nics for access to the host vs access to the guests. IN addition you'll likely want to cluster this box (unless uptime is not a concern) –  Jim B Jul 9 '09 at 18:55
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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".

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He's got a single server - so it's a single point of failure whether he used VMs or uses it as an all in one. –  Tubs Jul 10 '09 at 10:10
    
Ahh, right. Point taken. –  phuzion Jul 10 '09 at 11:08
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