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.

the Practice

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.