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"Virtualization is a proven software technology that is rapidly transforming
the IT landscape and fundamentally changing the way that people compute."
- VMware
To paraphrase a well-known politician, when it comes to adoption of virtualization,
there are things we know, things we know we don't know, and things we don't
know we don't know. This is pretty apt when we look at where we are with this
uniquely disruptive technology.
Factors such as consolidation, cost savings, dynamic provisioning, and migration
are driving most IT shops to experiment with some form of virtual machine product
today. In the U.S., this has moved from back-room toying and development environments
into full, public-facing application infrastructure systems. In Europe, many
medium to large companies are in early stage deployment and experimentation
mode.
There is good reason for this. We are feeling our way in partial darkness in
many ways. We know that there are clear benefits to be had, but Proof of Concepts
and lab experimentation are only indicative on certain levels; we don't know
how our networks will react once we scale up into full production.
Suddenly 40 physical servers become 400 virtual ones. How will your network
react? How will you manage the traffic flow to all those new IP addresses? Will
you rebalance manually every time you provision new servers? Of course not.
And what about your underlying data? Will you rebind the new virtual servers
to underlying storage assets every time you kick start a new virtual machine?
No.
For all of their benefits, virtual machines also add complexity, scale, and
management challenges. Implementing virtualization without considering its impact
on surrounding IT resources can lead to unexpected results. These critical areas
may appear either immediately or over time, potentially months or years later.
Knowledge is the first step to avoiding surprises and showstoppers during production.
What follows are the
seven challenges that accompany any major virtual platform implementation
or migration. Often these issues aren't seen during staging and testing and
only appear when the virtual machines are asked to take on the same production
load as physical machines. These pain points represent two cornerstones of the
data center: network and storage.
- Lack of performance and availability. Virtualization moves many
I/O tasks tuned for hardware back into software. I/O intensive applications,
like cryptographic processing applications for SSL, don't fare well when virtualized.
Performance issues and virtual machine saturation (too many virtual machines
running on one physical host) caused by virtual sprawl can cause application
and storage network resources to be depleted at a much faster, and often unanticipated,
pace.
- Lack of application awareness. One of the limitations of hypervisor-based
virtualization is that it only virtualizes the operating system. OS virtualization
does not virtualize, nor is it even aware of, applications that are running
on the OS. By adding an extra software management layer between the application
and the hardware, the applications may run into performance issues that are
out of their control.
- Additional, unanticipated costs. One of the primary drivers for virtualization
is cost reduction, driven by consolidating devices in the data center. But,
once virtualization hardware and software is acquired, operational expenses
can grow unbounded: headcount can increase or existing staff may require training
to administer the new virtual machine platforms.
- Unused virtualization features. It is often the case where these
new technologies perform flawlessly in development and staging but they are
unable to scale to production levels once deployed. First and foremost, network
storage is a requirement for virtual platforms that implement live machine
migration; direct attached and local storage will only work for running local
virtual machines.
- Managing explosive and unexpected growth. Although converting physical
machines to virtual machines is an asset for building dynamic data centres
(fluidity, disaster recovery, backups) virtual hard drives become extremely
large flat files -- a typical Vista Ultimate install consumes ~15 gigs of
local storage for the OS alone, not counting data files -- and storing these
files can quickly become unmanageable. In a recent report from Enterprise
Strategy Group, 54 percent of the customers surveyed reported some increase
in storage capacity specifically tied to OS virtualization and the installation
of virtual platforms. Eighteen percent of responders reported an increase
of physical storage greater than 20 percent beyond their storage needs for
physical servers.
- Congested storage network. Planning large virtual machine migration
moves can be a challenge to keep from flooding the storage network, and is
virtual sprawl and unmanaged virtual machines begin to appear in the data
center, unplanned virtual machine migrations can literally bring the network
to a stand-still, even on a LAN.
- Management complexity. Overlapping all portions of the data center,
managing virtual machines as part of the complete management solution can
be a struggle at best. If you are already using tools to manage the application
and operating environments of each physical machine, by either using clients
on the systems or by measuring application metrics on the wire (such as latency,
response time, etc), management of the virtual machines themselves doesn't
have to change.
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