Virtualization, Blessing Or Curse?

Managing virtualization at a large scale is fraught with hidden challenges.
BY eVanGeLos kotsoVinos

Virtualization: Blessing or curse?
touted as the solution to many challenging problems, from resource underutilization to data-center optimization and carbon emission reduction. However, the hidden costs of virtualization, largely stemming from the complex and difficult system administrationchallenges it
V I Rt Ua L I Zat Io N I S o f t eN
poses, are often overlooked. Reaping the fruits of virtualization requires the enterprise to navigate scalability limitations, revamp traditional operational practices, manage performance, and achieve unprecedented cross-silo collaboration. Virtualization is not a curse: it can bring material benefits, but only to the prepared. Al Goodman oncesaid, “The perfect computer has been invented. You just feed in your problems and they never come out again.” This is how virtualization has come to be perceived in recent years: as a panacea for a host of IT problems. Bringing virtualization into the enterprise is often about reducing costs without compromising quality of service. Running the same workloads as virtual machines (VMs) on fewer serverscan improve server utilization and, perhaps more importantly, allow the deferral of data-center build-outs—the same data-center space can now last longer. Virtualization is also meant to enhance the manageability of the enterprise infrastructure. As virtual servers and desktops can be live-migrated with no downtime, coordinating hardware upgrades with users or negotiating work windows is nolonger necessary— upgrades can happen at any time with no user impact. In addition, high availability and dynamic load-balancing solutions provided by virtualization product families can monitor and optimize the virtualized environment with little manual involvement. Supporting the same capabilities in a nonvirtualized world would require a large amount of operational effort. Furthermore, enterprisesuse virtualization to provide IaaS (Infrastruc61

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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 rollingout an application sooner can provide first-mover 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 fromand 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-balancingsolutions—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...