Management hurdles

Other issues arise when managing the virtual infrastructure itself. The management tools offered by the vendors tend to be works in progress. For example, Ixis' Van Der Walt has found managing remote servers with VMware's Virtual Center management platform to be problematic. "VMware is good at managing local infrastructure, but you usually have to have a VirtualCenter Server at each datacenter. I'd like to be able to manage the whole infrastructure with one server," he says.

Computer Sciences Corp. (CSC) also found that backing up virtualized physical servers to tape had its challenges. "It came down to whether we should use traditional backup for each virtual server or use VMware's tools to do the backup and back up virtual machines as files," says John Macioci, partner and deputy CIO of CSC. The company found VMware's tools to be overly complex and decided to settle on traditional backup solutions from Veritas, treating each virtual machine as an individual server. (Arvato's Loesche, on the other hand, has high praise for Virtuozzo's backup tools.)

And even when the physical server load is reduced, you still have all those virtual servers to monitor and patch. This is where host-based virtualization platforms, such as Solaris Containers or Virtuozzo, have advantages. "Since all the VM file systems are accessible from the hardware node, you can update them all with one small script," Loesche says. The drawbacks, compared with hardware emulation systems such as VMware's ESX Server and Microsoft's Virtual Server 2005, are that you can't mix different operating systems on one hardware node, and if a bug crashes the kernel, the entire server crashes.

In fact, hardware failure is a big issue with virtualization, as a single failed physical server can bring down all the resident virtual servers. The threat can be offset, however, by the ability to move a virtual machine to new server hardware quickly if you can detect imminent failures before they happen.