Server Virtualization Quiz

How much do you really know?

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The correct answers, according to experts, are as follows:

1. [a] Server virtualization software imposes no constraints on the versions of the Windows Server operating system (or Linux) that you place in each virtual machine, although a completely new version of Windows may require that you check for compatibility with your server virtualization software before you install it.

2. [a] Rebooting a virtual machine can be done without touching the physical machine or the server virtualization software. It has no effect on the other virtual machines; they are completely isolated from one another. Note, however, that if you reboot the physical machine (that is, you reboot the server virtualization software), it will disrupt the operation of all the virtual machines.

3. [a] In general, it is better to install a mix of heavy-workload and light-workload applications on each physical server in order to make the best use of the server. The heavy-workload applications will benefit, in terms of performance, from being able to momentarily use a large part of the server's CPU and memory resources during traffic peaks, and the light-workload applications will effectively get a "free ride" on the server.

4. [b] There is nothing technically wrong or difficult about placing server virtualization software on blade servers. However, this practice should not be pursued without careful consideration of the concentration of risk that it entails. For example, if you build 10 virtual machines on each of 16 blade servers, the total number of applications running in the blade-server shelf could be 160. If anything bad happens to the shelf (fire, power loss) and adequate backup or redundancy (outside of the shelf) does not exist, you will simultaneously lose 160 applications, potentially devastating your business.

5. [b] You should have already established a SAN in the data center or have extended SAN services to the servers that you are considering as candidates for replacement by virtual machines. If not, it is very likely that the aggregate storage demands of the applications or databases running on each virtualized physical server will exceed what can be provided on hard drives within the server.

6. [c] Even without the potentially worrying combination of blade servers and server virtualization, use of server virtualization on standard servers puts several eggs in one basket. Given that hardware failure in one server will take out, say, 10 applications and/or databases, it is generally desirable to provide some level of redundancy, permitting the entire contents of the server to be quickly moved to a standby server if the main server fails.

7. [b] It is generally better to designate physical servers as "development," "test/QA" and "production" and to place instances of applications and databases on them accordingly. This policy is driven by security needs and, in some industries, by regulatory considerations dictating different treatments for the different environments (particularly for production).

8. [c] In an ideal data center, it would be no harder to keep track of software licensing for virtualized servers. Real-world experience, however, shows that it is indeed harder. In a virtualized environment, the ease with which virtual machines can be created -- combined with the difficulties of finding out from business groups exactly what software is required on, or has been installed on, each virtual machine -- makes tracking license requirements and license usage significantly more difficult.

9. [c] Adequately securing access to, and information stored on, virtual machines presents new challenges, over and above those in a traditional environment. First, access to the virtualization software must be very tightly controlled. Second, anyone with access to a virtual machine can download an application that mounts an attack on the virtual "walls" that isolate one virtual machine from the other virtual machines. Third, it is more complex to implement access restrictions at a network level for each individual virtual machine, so network-based security may end up being set at that of the least-sensitive application running on a physical machine (particularly if the network/firewall management team is busy).

10. [c] Although numerous suppliers of software for CMDBs have started to embrace server virtualization, there are many older versions of CMDB products implemented in data centers. These may not have the necessary underlying database designs that recognize a virtual machine as a "data entity" and can represent the relationship "Virtual Machine A is on Physical Server X." Many of the things that go with a physical server -- such as the version of the operating system installed on it, and its IP address -- must now be associated with a virtual machine. In addition, these things must be associated with nonvirtualized servers. These requirements mean that the database design underlying a CMDB requires a major overhaul for the product to have any hope of being useful to a data center that has started to introduce virtualization.

11. [c] Once IT tells business groups that it can provision a new virtual machine within a few hours, human nature tends to take over. Businesses go berserk, submitting requests for virtual machines that they might have hesitated to ask for if they had to wait for physical hardware to be budget-approved, ordered, delivered, installed and made ready for use. Some experts call the result "VM sprawl." Worse still, when a project is canceled or the development work is completed, can business groups be relied on to tell IT that the virtual machine can be deleted? Of course not.

12. [b] The largest part of the work done in a data center tends to be driven by the number of "servers," and it makes no difference whether these are standard servers or virtual machines. Each virtual machine requires the same level of attention as a standard server when it comes to responding to trouble tickets, managing operating system and application updates and patches, managing security issues, monitoring performance and so on. The small reduction in total work achieved by not having to install physical machines as often as you once did tends to be offset by the extra work involved in installing and configuring server virtualization systems such as VMware on each new machine.

Hamer is a director at Acumen Solutions, a business and technology consulting firm with offices across the U.S. and Europe. Contact him at

This version of this quiz originally appeared in Computerworld's print edition.

Copyright © 2009 IDG Communications, Inc.

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