Network Appliance last week joined companies offering virtual-tape library appliances, seeking to differentiate itself with load balancing and tape optimization.

The company announced two disk-based appliances - the NearStore VTL600 and VTL1200 - that store as much as 168TB of data. The products are based on technology obtained via Network Appliance's buyout last year of Alacritus.

Like makers of other virtual-tape libraries, Network Appliance uses disk instead of tape to back up and recover data faster and save on media-acquisition costs and floor space occupied by spacious tape libraries.

The NearStore VTL600 has a single controller, while the VTL1200 has two. As data gets older, the devices can copy it directly to physical tape.

The NearStore VTLs work with traditional backup software from BakBone, CA, CommVault, HP, Legato, Symantec, Syncsort and Tivoli. They work with tape libraries from ADIC, IBM, Quantum and Sun. The appliances can back up data on any vendor's open systems storage device, the company says.

''The VTL is an opportunity for them to break out into heterogeneous environments," says Stephanie Balaouras, senior analyst at Forrester. An existing NearStore archiving appliance is designed for use with other Network Appliance gear, she says.

Many storage companies have embraced virtual tape libraries as a way to quickly back up and recover data. Among them are large storage and systems vendors, such as EMC and HP, and a host of smaller and newer companies, including Copan Systems, Diligent, Data Domain, FalconStor, Maxxan, Neartek and Sepaton.

Unlike such competitors as EMC's Clariion Disk Library or IBM's Virtual Tape System, the NearStore VTLs use a self-tuning technology to balance workload to their physical disks. They also have a technology Network Appliance calls Tape Smart Sizing, which allows the VTL to save as much as 50% of the media used during backup to tape library operations.

"The NearStore VTL lets administrators create tapes in native format of the backup application if you need to recover from tape in the future," Balaouras says. ''It also supports a one-to-one mapping of virtual to physical tapes, so they can optimize the compression of data on tape and increase efficiency."

Virtual-tape library technology is popular in mainframe environments, where it can save floor space and media-acquisition costs. IBM, Sun and Diligent offer mainframe-based virtual-tape products, and Sun has announced its intention to expand its Virtual Storage Manager into open systems.