The World of Hierarchical Storage Management

Susan Colwell

Data that's archived to off-line storage devices may rarely be needed, but network administrators still must identify, move, and maintain it. To do this effectively, they need a special method for managing off-line storage.

Hierarchical storage management (HSM) automatically and transparently migrates data from a file server's hard drive to less-expensive near-line or off-line storage (see the figure "Storage Hierarchy" ). When files are migrated, stub files are left in primary storage as placeholders; thus, all files remain visible in the network file system, and you can still view and access them.

Five industry-accepted guidelines, or lev els, help define HSM: automatic migration of files with transparent retrieval; real-time, dynamic load balancing of free disk space based on predefined thresholds; management of layers of storage hierarchy with dynamic balancing; migration of files based on data type through the use of policies; and object management support.

Several companies--including Cheyenne Software ((516) 465-4000), IBM ((800) 426-2255), Platinum Technology ((708) 620-5000), Seagate Software (formerly Arcada and Palindrome; (407) 333-7500), and Wang Software ((303) 444-4018)--support most, if not all five, levels. IBM's AdStar Distributed Storage Manager (ADSM) is one of the few storage solutions that supports a wide variety of platforms and all five HSM levels. Recently IBM announced support for Windows NT on the server side and an optional automated disaster-recovery plan. (For more on HSM-related software, see "Network Storage Economizers," March 1995 BYTE.)

With an HSM solution, you can potentially decrease physical sto rage expenses, reduce storage management costs, quicken data access, increase end-user productivity, optimize use of storage devices, and speed data backup. Installation and setup may be monumental, but the benefits make it well worth it.

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Storage Hierarchy

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