Servers

10 issues to consider during virtualization planning

Virtualizing your servers offers significant advantages, but effective planning is crucial to your success. Make sure you have satisfactory answers to these key questions before you get underway.

Virtualizing your servers offers significant advantages, but effective planning is crucial to your success. Make sure you have satisfactory answers to these key questions before you get underway.


Server virtualization is becoming increasingly popular, and it seems that everyone is in a mad dash to virtualize their datacenter.  While there's no disputing the benefits of server virtualization, there are some questions you should address before you begin to virtualize your servers.

Note: This article is also available as a PDF download.

1: Does my virtualization plan include a single point of failure?

I recently did a consulting job for an organization that had virtualized all of their servers. The problem was that they'd placed all of their virtualized domain controllers onto a single host server. If that host had died, it would have taken all the domain controllers with it. It's important to plan your virtual server deployment so that the failure of a single host server will not have catastrophic consequences.

2: Are all my applications supported in a virtual environment?

Believe it or not, some fairly common applications are not supported on virtual servers. For example, some versions of Exchange Server are supported only on physical servers. Others are supported only on specific virtualization platforms. Before you begin virtualizing your servers, make sure that your applications will be supported in a virtual environment.

3: Do I have any servers that are not good virtualization candidates?

Some servers simply do not make good virtualization candidates. This is especially true of servers that run resource-intensive applications or that require special hardware. For example, some enterprise applications enforce copy protection through the use of a dongle. Dongles are almost never supported in a virtual environment.

4: How will domain controller placement work?

Earlier, I mentioned that you shouldn't place all of your domain controllers on a single host, but there is more to domain controller planning than that. You have to consider whether you want to virtualize all your domain controllers. If you do virtualize all of them, you will have to decide whether the host servers will be domain members. Making the host servers domain members when all of the domain controllers have been virtualized leads to a "which came first, the chicken or the egg" paradox (although it can be done).

5: What is the most suitable virtualization platform?

Numerous server virtualization products are on the market, and each has its own strengths and weaknesses. Be sure to take some time and figure out which product will work best for your own situation.

6: What is the contingency plan if a host server dies?

While a server failure is never good, its effects are compounded in a virtual environment. A host server failure can take down several virtual servers and cripple your network. Because host server failures can be so disruptive, you need to have a plan that will help minimize the impact of an outage.

7: How many guest machines can each host accommodate?

Probably the single biggest mistake administrators make when virtualizing a datacenter is overloading the host servers. It is critical that you do some capacity planning ahead of time to determine how many guest machines each host server can realistically accommodate. Since every guest machine is different, you need to at least have an idea of where you would like to place each guest machine when you begin the capacity planning process.

8: What software licenses will be required?

Software licensing often works differently in a virtual environment. For example, if you are using Hyper-V, you may not be required to license the Windows operating systems that are running on your guest machines. Things aren't always so cut and dried, though, because the actual license requirements vary depending on the versions of Windows being used. Make sure that you understand the license requirements for the operating systems and applications that will be run on your guest machines.

9: How will the old server hardware be used?

The virtualization process often results in a number of leftover servers. You might be able to repurpose some of them as virtualization hosts, but you might end up having to retire them. In any case, you should have a plan for your old server hardware.

10: What is the plan for existing server clusters?

Although cluster nodes can sometimes be virtualized, you may find that the nodes perform better on physical hardware. If you do decide to virtualize your cluster nodes, just make sure that you don't put all of them on the same host server. Otherwise, you will defeat the purpose of having a cluster because the host will act as a single point of failure.


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About

Brien Posey is a seven-time Microsoft MVP. He has written thousands of articles and written or contributed to dozens of books on a variety of IT subjects.

11 comments
m_esso
m_esso

Backing up your VM's in an intelligent manner can be challenging. You can save yourself a lot of time (on a restore) by backing up the 'images' of your VM's instead of their contents. Depending on the OS used for both the host & guest, there are a few good options and a lot of questionable ones in between. Do your diligence!

SANman31
SANman31

This article forgets to point out one of the most critical issues to think about when implementing virtualization projects: The management and performance optimization tools. VMware has some good basic managment tools, but is very weak on the performance optimization tools side. Implementing applications on virtual machines is relatively easy, but ensuring they have good performance is a major challenge. This is especially true for I/O intensive applications like databases, which if not properly implemented can bring the SAN to its knees very quickly. Check into tools like Virtual Instruments VirtualWisdom to see a best of breed solution.

Mycah Mason
Mycah Mason

Thanks for the info. For someone without any VM experience, what are some good resources to get started with the basics? Virtualization makes a lot of sense conceptually, but it seems that there is a LOT to consider when implementing this solution. What recommendations do you have for getting some experience?

tr
tr

I'm surprised there is no mention of backup plans. It seems to me there is a big hole in this technology with backing up VMs. There are the standard backup methods that can be used within the VM, but to take full advantage of the technology you need to copy that entire VM. If you are not able to bring the server down to copy the VM for business reasons (24x7) there is software for live backups, but it is expensive and flaky from my understanding.

radio1
radio1

In point #1 you mention the single point of failure. I just wanted to add Don't forget the san. If you choose to virtualize using High Availiblilty or Motion capabilities, you will require a single point of storage. I find it interesting that some of the best reasons to go virtual is to reduce single points of failure, yet we do so by using common storage devices. I understand that you can purchase 2 sans and implement some replication between the 2 and even have those auto failover with some vendors. some even support off site replication over wan links. I am just mentioning to be awar of this and to plan accordingly. Like one person mentioned. Go cheap in the beginning, pay for it in the end.

ppeeters
ppeeters

We use a USB over ethernet device for virtualized servers that require a USB dongle to control software licenses. We also use a RS232 over ethernet with works just as well for serial devices.

ppratyush
ppratyush

Good article. A comment, under point#3 above regarding enterprise application making use of dongles for copy protection - Dongle works pretty well in virtualized environment. The virtual machines are supporting USB devices plugged to physical machines and so does the USB dongles. Same USB device can not be accessed from different virtual machines simultaneously and so does the USB dongle (which is good from copy protection standpoint).

simon.rowe
simon.rowe

Good article. One thing I would add, being about 6 months after our first wave of server virtualisation, is that you soon start to think of other jobs that new virtual servers could do for you, and so does everyone else! If you are not careful, suddenly everyone in the organisation 'wants a virtual server to do XXX' and you no longer have the excuse that they are all busy or overloaded because they rightly point out that you can create a new server very easily. Having got this far in our process, I would advise anyone starting this to plan for a large injection of virtual disk space, and maybe another host server or two about 6-12 months in. Then you can carry on providing as the demand picks up. Hope this is helpful. Simon

neil_willet
neil_willet

There are some difficult backup solutions out there but there are some good and relatively cheap ones as well. SAN Snapshot aware solutions would be a first choice if possible. vRanger is a good alternative for backups and is not complicated or expensive.

WiseITOne
WiseITOne

I agree, a SANS and the HOST can be failure points of an entire virtualized environement. I do think the cost savings from hardware and electricity use outway the costs and an ROI can be expected within a few years depending on your build. It is vital that failovers are put in place. It is also important that SQL servers or databases be tested in a sandbox before you try and move them over as these database servers usually are not the best candidates for virtualization. It would have been cool for companies if we didn't have to license everything, I know software companies need to make money and it isn't fair to them, but it would have saved a ton of more money.

grifs71
grifs71

Yes, that is correct, with a new SAN and Server Environment everyone and their brother in law wants to do something with the space or wants their VM's. Physical servers are a single point of failure, unless you have a bare-metal rebuild in place to do it quickly. Visualizing servers is the best thing to do in order to have HA, but you need to invest in VMware with licensing to allow you to lose a host and move on with life. You can go cheap, but it will cost you more in the end.