The world of the virtualized data center is going to get increasingly complex. That's in part because, to get the virtual environments they want, IT managers are going to have to mix and match many of the pieces themselves.

Some routine functions, such as mission-critical data backup and recovery, are uncharted waters for early virtualization converts. Both VMware and Citrix Systems offer backup and recovery features, but they're for the virtual machine image itself, not the data being used by the application running inside the VM. Guaranteeing the live data means going to third parties, such as Hewlett-Packard or Marathon Technologies.

At VMware's VMworld in Las Vegas this week, HP will announce that the Zero Downtime Protection feature of its Data Protector product now safeguards data for apps running on VMware ESX virtual machines. It does so by taking periodic snapshots, providing near continuous data protection.

In the physical world, it's often taken for granted that the data is being backed up. In the world of VMs, host servers are so fully utilized that there are few resources left to do data backups, says HP's Jen Tisevich, product marketing manager for Data Protector. The rub: Companies need to use the HP Enterprise Virtual Array storage system to take advantage of the feature.

HP is just one of the vendors that's adding value--and complexity--to the consolidated, virtualized server. At VMworld, Citrix will announce version 5 of its XenServer hypervisor. To achieve 99.999% availability, XenServer 5 can be combined with Marathon's EverRun high-availability product for application failover and data preservation while running VMs, says Simon Crosby, CTO of Citrix's XenSource division. But you need to be a XenServer 5 Enterprise- or Platinum-level customer for the two to work together.

Want virtual machines in different locations, spreading risk while combining resources? Sun Microsystems is folding a Web server into its xVM server hypervisors so they may be managed remotely through a browser window. Companies could generate an internal cloud data center through such virtualized resources, says Steve Wilson, VP of xVM. An agent in xVM can contact Sun's Ops Center management software, which will provision VMs, assign workloads, then return them to storage in a remote location.

Some complexities are just starting to surface. If you're considering managing lots of virtual machines as a virtual data center, and operating under a service-oriented architecture, what might that mean for your services to partners and customers? Part of the application is in a VM on one server, part on another. In a virtual world, how do you get a consolidated view of an enterprise application?

Nobody's talking about that yet, with the possible exception of little-known, 2-year-old BlueStripe, whose FactFinder product is designed to discover and map dependencies of SOA-type applications in VMs, then present a consolidated view of application performance. In its first iteration, it only tracks application pieces running in VMware virtual machines.

The big vendors are starting to tout their management software's ability to manage VMs from multiple vendors. But to get all they want, from backup to visibility, IT managers for some time will be cobbling together their own combinations.