Storage vexations of server virtualization

Computerworld - Server virtualization offers a host of efficiencies, but storage administrators say it may open a can of worms on the storage side. Resulting headaches can include huge I/O bottlenecks for primary and backup storage, as well as complicated disaster and recovery efforts, among other things.

With multicore CPUs being utilized to create multiple virtual machines on servers -- and since the typical large-enterprise server farm is 70% to 80% virtualized -- there's a lot more application I/O moving back and forth between application servers and primary storage, and between primary storage and backup storage.

What's more, between 2000 and 2010, the number of servers worldwide multiplied by a factor of six, while the amount of storage increased by a factor of 69, thanks to server virtualization, according to researchers at IBM.

In July, Computerworld polled dozens of storage administrators to find out how server virtualization has complicated their work lives. Our findings yielded this list of five top headaches. But fear not: IT analysts and virtualization veterans offer their advice on how to deal with each challenge.

1. Storage Performance Slowdowns and I/O Bottlenecks

IT administrators are painfully aware that storage performance is growing at a much slower rate than computing power. So when it comes to virtualization, it's no surprise that I/O bottlenecks and slow storage performance are the No. 1 problem for one-third of the administrators who responded to the Computerworld poll.

"Virtualization lets you do a whole lot of workloads on one physical piece of hardware, but there's lots of different I/O [operations] mixed into the I/O stream, so it makes disks work harder and caching less effective," says Jeff Boles, senior analyst at Taneja Group in Phoenix. "Virtualization lets us easily do more than our compute power is capable of."

How to deal: The solution to the I/O bottleneck depends on where the problem lies: in the network or in the storage domain. Most often, it's in the storage environment, because improvements in storage capability have lagged behind that of all other infrastructure. "You have a very slow, creeping, linear progression of storage capability. Rotating disks can only go so fast. Part of the problem is visibility. Administrators can't see what's going on inside the storage environment, so they don't know how to fix it. Fortunately, we're getting some tools that can help you figure out that problem and address it [more easily]," Boles says.

Fibre Channel customers, for instance, might use Virtual Instruments' performance monitoring tool for storage area networks (SAN) to optimize performance and availability. Other storage vendors delivering visibility tools include NetApp, which recently acquired Akorri and its predictive tool for the virtual infrastructure, and EqualLogic, which has a graphical user interface that lets customers monitor storage system performance.