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But be warned: This is an undertaking fraught with peril! Comprehensive Hierarchical Storage Management (HSM) systems are complex and can be difficult to implement well. At Novell's recent BrainShare conference, a presenter asked for a show of hands from the large audience of NetWare administrators to see how many had implemented the free HSM system included with NetWare 4.x. Few hands were raised, and the presenter wasn't surprised.

Storage management can include backup software, HSM, storage policies, or archival software/hardware to storage device management and disaster-recovery mechanisms and other components, so defining it can be difficult. This Buyer's Guide focuses on products that manage storage by letting administrators set watermarks for migration of files from primary magnetic disks to secondary and tertiary storage systems, including magneto-optical (MO) erasable jukeboxes and tape libraries.

In selecting a storage management solution that's right for your organization, you must take all of these things into account. The idea is to move infrequently used files to media that is cheaper per megabyte than hard disk media. Doing so will free more expensive and faster media for more day-to-day files.

A typical HSM hardware setup includes pr imary storage on hard disk, secondary storage on MO erasable jukeboxes (where files with only occasional access are stored) and tertiary storage using tape libraries (where files that seldom get accessed are stored). HSM systems can dramatically expand the amount of storage space available from megabytes to gigabytes and from gigabytes to terabytes. By using media that has a per-megabyte cost that is less than a hard drive's cost, an HSM system can reduce the overall cost of storage from as much as 50 cents per MB to as little as pennies per MB.

Many HSM vendors supply backup software that knows about the "stub" file stored in primary storage. This file points to the real, migrated file on a migration device. The vendor's program knows to back up the stub without demigrating the real file. Some HSM vendors certify that third-party backup software will work with their software. If you don't want to change your present backup system, pick a vendor whose products will work with your existing backup softwar e.

Other than slower access to migrated files, users won't notice much difference because a stub file or placeholder will be retained in the file system that points to the migrated file. Users will still see the file listed during directory operations. When they access a migrated file, it is placed back in main storage.

Where to Start You'll need to consider a number of factors when you investigate the purchase of an HSM system. First and foremost, be certain that the system supports all of your platforms. Don't forget to include more pedestrian operating systems like Windows and Macintosh. As the Buyer's Guide charts show, there are products available that will manage storage on your client OSes, and you must decide if you will use this feature.