ture as a Service) cloud offerings that
give users access to computing resources on demand in the form of VMs.
This can improve developer productivity and reduce time to market, which is
key in today’s fast-moving business
environment. Since rolling out an application sooner can provide first-mov-er advantage, virtualization can help
boost the business.
Although virtualization is a 50-year-old
technology, 3 it reached broad popularity only as it became available for the
x86 platform from 2001 onward—and
most large enterprises have been using the technology for fewer than five
years. 1, 4 As such, it is a relatively new
technology, which, unsurprisingly, carries a number of less-well-understood
system administration challenges.
Old Assumptions. It is not, strictly
speaking, virtualization’s fault, but
many systems in an enterprise infrastructure are built on the assumption
of running on real, physical hardware.
The design of operating systems is
often based on the principle that the
hard disk is local, and therefore reading from and writing to it is fast and
low cost. Thus, they use the disk generously in a number of ways, such as
caching, buffering, and logging. This,
of course, is perfectly fair in a nonvirtualized world.
With virtualization added to the
mix, many such assumptions are
turned on their heads. VMs often use
shared storage, instead of local disks,
to take advantage of high availability
and load-balancing solutions—a VM
with its data on the local disk is a lot
more difficult to migrate, and doomed
if the local disk fails. With virtualization, each read and write operation
travels to shared storage over the network or Fiber Channel, adding load
to the network interface controllers
(NICs), switches, and shared storage
systems. In addition, as a result of consolidation, the network and storage
infrastructure has to cope with a potentially much higher number of systems,
compounding this effect. It will take
years for the entire ecosystem to adapt
fully to virtualization.
System Sprawl. Conventional wis-
dom has it that the operational work-
load of managing a virtualized server
running multiple VMs is similar to that
of managing a physical, nonvirtualized
server. Therefore, as dozens of VMs can
run on one virtualized server, consoli-
dation can reduce operational work-
load. Not so: the workload of manag-
ing a physical, nonvirtualized server is
comparable to that of managing a VM,
not the underlying virtualized server.
The fruits of common, standardized
management—such as centrally held
configuration and image-based provi-
sioning—have already been reaped by
enterprises, as this is how they manage
their physical environments. There-
fore, managing 20 VMs that share a
virtualized server requires the same
amount of work as managing 20 physi-
cal servers. Add to that the overhead of
managing the hypervisor and associ-
ated services, and it is easy to see that
operational workload will be higher.