Choosing the right disk-based backup system

Three years ago, there wasn't a disk-based backup market. Besides a pair of niche mainframe solutions, only a couple of small companies tried to convince information technology managers that inexpensive disk drives for desktop PCs could be linked to make a suitable platform for backing up enterprise data on servers. Big storage vendors dismissed the notion at the time.

Since then, many IT shops have added disks to their backup routine and drastically reduced the time to complete a backup compared to backups using only tape, and the sky hasn't fallen. With similar success stories, disk-based backup wares have now become a hotbed of activity in the storage market, with scores of products offered not only by start-up firms but also by large industry incumbents.

There are many approaches to using disks for backup, but the products generally fit in one of two categories, said Dianne McAdam, senior analyst and partner at the research and advisory firm Data Mobility Group LLC:

n Virtual tape — With these products, the disk array system looks and behaves like a tape drive to the servers that are initiating a data backup or restore operation. An advantage of this approach is that IT managers do not usually have to modify the off-the-shelf backup software they use because the software still thinks it's writing to tape, not disks.

However, because data is written in a tape image, during a data restore operation it must be converted back to disk, an added step that some IT managers might want to avoid, McAdam said.

Vendors that offer virtual tape solutions include Diligent Technologies Inc., EMC Corp., Neartek Inc., Quantum Corp., Sepaton Inc. and many others.

n Disk-as-disk — These systems do not emulate tape drives. Instead, they use one of a variety of techniques for saving data to a disk-based backup system in a disk-friendly format. This approach usually allows for more frequent data copies and eliminates the need to convert a tape image back to disk during a data restore, likely speeding up the process, McAdam said.

The downside is that disk-as-disk might require more configuration and management chores associated with the disk-based file systems.

Vendors that offer disk-as-disk solutions include Avail Solutions LLC, Network Appliance Inc., Nexsan Technologies, Revivio Inc., Storage Technology Corp. and others.

Some vendors' products, including several of those named above, can be used in either mode.