To virtualize or not to virtualize? Before deciding, take a close look at this technology's hidden costs.
In
the rush to consolidate servers and save precious data center space,
many companies are turning to virtualization. By consolidating a data
center's physical servers into virtualized servers, the enterprise can
experience higher server utilization and increased operational
efficiency.
Although virtualization brings lots of benefits and features, it is
important to keep in mind that virtualization is not the Holy Grail and
may not be appropriate for every situation or environment. It does come
with some drawbacks. These drawbacks may not be deal breakers, but you
should be aware of them before you adopt the technology. In this
column, we will look at several key issues that can cause problems in a
virtualization adoption.
Part one will discuss the power and heat costs and the management concerns of virtualization. Part two will discuss networking issues and the problem of virtual machine sprawl. Finally, part three will discuss licensing, performance and storage.
With that out of the way, let's get started.
Power and heat costs
One of the first problems often overlooked is the high power
consumption and high heat output of a physical server hosting multiple
virtualized servers. Remember that virtualized servers cause the
hardware to run at a higher utilization rate, which means the power
required to operate the physical server hardware goes up, as does the
heat output.
A physical server running many virtual machines may run at a
constant 80% or higher utilization rate, at which point the hardware is
pulling quite a bit more power than a non-virtualized server running on
average around 15% utilization.
Many data centers are not equipped to deal with the new power
requirements that are necessary to support virtual servers. For
example, you might need four 20-amp power circuits for each 42U data
cabinet that is fully loaded with standard 2U servers, in order to
satisfy power needs and to provide power redundancy (the ability to
withstand a single circuit failure). This power scheme is actually
double the standard power layout, which provisions only two 20-amp
power circuits per cabinet.
And doubling the power per cabinet poses new problems of its own,
especially if it means the data center needs to upgrade its whole power
infrastructure.
Management
Virtualization also raises new management concerns, especially
in the areas of patching, backup, host provisioning, security,
monitoring and hardware requirement.
Patching
In a large virtualized production
environment, it can be a challenge to apply software patches to both
the physical host servers and the virtual machines. If system reboots
are required, it impacts business a whole lot more to take down a
physical machine hosting hundreds of virtual servers than it does to
reboot a machine that serves as only one server.
So while in a non-virtualized environment, a company may not have to
significantly plan for downtime around a Windows Update patch, in a
virtualized environment, patching and rebooting a single host server
creates a much more significant impact. Planning downtime around
something as simple as patching becomes an arduous task. Companies
running large enterprise environments with hundreds of virtualized host
servers face a complicated maintenance window, leading some to apply
only the most critical patches which leaves them in a more vulnerable
state.
Some companies, such as Internet Security Systems (ISS), offer
virtual security patch technologies to protect servers without having
to go through the actual patching process. This does not, however,
resolve the problem of applying stability or bug patches, which have to
be applied on the physical server. In these cases, reboots are
unavoidable.
The bottom line is that physical server reboots can be very costly in virtualized platforms.
Backup
Implementing a sound backup solution in a virtualized environment is
another major pain point. The first obvious question is what data do
you want to backup, which is then quickly followed by how often? Is the
answer backing up your entire virtual disk repository and all disk
images? Or perhaps you should consider only backing up the base images
and then the various REDO or undo disks?
Either way, you could be facing an uphill battle. The sheer amount
of data needing to be backed up can be staggering. Unless the company
is lucky enough to have a very robust SAN or some kind of a
backup-to-disk solution, backing up many terabytes of data to tape is
way too slow and inefficient, and we still haven't even considered how
to go about backing up the physical host server or its operating system
configuration.
Provisioning
Automated physical host provisioning is highly desirable and can cut
down drastically on the physical server deployment time. But physical
server provisioning is only half the battle. We have to consider
automated provisioning of the virtual servers once the physical host
server is up and running and fully configured.
Many technology companies provide an automated solution for
deploying and provisioning physical servers. Many of those same
companies, such as Altiris, are now capable of automatically
provisioning virtual servers as well. But the process can be complex,
especially if your organization has a heterogeneous virtualization
environment with multiple virtualization platforms such as VMware and
Microsoft Virtual Server. The additional complexity of automating both
a physical and virtual environment has to be carefully weighed and
considered.
Security
Security issues are more complex in a virtualized environment because
you now have to keep track of security on two tiers: the physical host
security and the virtual machine security. If the physical host
server's security becomes compromised, all of the virtual machines
residing on that particular host server are impacted. And a compromised
virtual machine might also wreak havoc on the physical host server,
which may then have an ill effect on all of the other virtual machines
running on that same host.
Monitoring
Monitoring is another critical area in which virtualization has its own
set of challenges and unique problems. You will have to monitor both
the physical servers and the virtual machines to make sure that your
environment is fully operational, since losing a physical host server
translates to losing several virtual machines.
Running monitoring software or agents on the physical host server
can potentially cause a negative impact to the performance of the
virtual machines by taking away valuable memory and CPU cycles that
would be consumed by the virtual machines. It's important to calculate
the percentage of physical resources used by the monitoring software to
see if you can spare those resources.
Other hardware
Finally, it is not uncommon to require multi-port network adapters and
several physical connections to each virtualization host server. Expect
three to four network ports to be cabled on each server, especially if
you are running a virtualization platform that does not offer the
ability to trunk multiple VLANs across a couple of physical channeled
links. This introduces yet another management problem; your environment
will be consuming a lot of Ethernet cables and your switch-port burn
rate will be pretty high. Expect to purchase a lot of access layer
Gigabit switches to handle your virtualization hosts.
About the authors: David Marshall is a
senior member of the reference architect team at Surgient, Inc., and he
specializes in server virtualization, virtualization applications and
Windows administration. He also runs the InfoWorld Virtualization
Report, as well as the virtualization news blog, VMBlog.com. David is also a co-author of Advanced Server Virtualization: VMware and Microsoft Platforms in the Virtual Data Center, a book that details years of hands on experience using and implementing server virtualization solutions.
Dan Knezevic is a senior network engineer and a team lead for
the data center operations team at Surgient Inc, providing expertise in
the data center network and server infrastructure as well as
virtualization platforms. He also specializes in network security and
enterprise storage solutions. He brings six years of virtualization
integration experience in the data center environment.
