Then there is the matter of what to back up -- each virtual server individually, or the physical server on which they run. Syncsort Inc.'s Backup Express lets users select either mode.

There is also the option of backing up the entire virtual server as a single file. "This method requires fewer backup agents on the virtual machine but is not application-aware," says Kelly Harriman-Polanski, director of product marketing at CommVault Inc. in Oceanport, New Jersey. "It also requires backup of very large files, which are typically 2GB in size or larger, unless the administrator takes the time to execute an export command to convert the file and zero-out the unused portions of the file."

According to Brian Wistisen, senior product manager in Symantec Corp.'s data management group, the main challenge lies not with the backup itself, but with the process of converting between the virtual and physical environments.

"This is where many solutions face the realities -- and dependencies -- of dealing with all the various low-level hardware devices and drivers necessary to operate the system effectively," he says, "particularly when converting from a virtual state to a physical one."

Most companies are adopting a multi-layered approach to backup. Suffolk University, in addition to using replication, has tape backup for off-line storage and is testing True Image software from Acronis Inc. as a way to achieve real-time imaging. Machettira says traditional tape is the university's third or fourth layer of backup.