Introduction to HSM

Hierarchical storage management was originally developed to reduce storage and management costs on mainframe and miniframe systems, and it is now helping manage data on LANs.

In a LAN environment, the need for sophisticated data management is increased by the network wide performance degradation caused by a near capacity disk.

HSM: a long term storage solution

As systems will always require more disk space, no matter how much excess capacity it seems when acquired, the challenge has been traditionally solved by one of three methods:

Buy More Disk

This solution does solve the problem, but at a high cost, currently in the range of C$300 per Gigabyte for the drive alone. With cables, controllers, and physical overhead the costs can add up, and the ongoing management costs continue to grow as well as capacity.

Have Users remove "unused" Files

The typical decree from the network manager for the users to clean up their own files, sometimes accompanied by a threat. Although this method does not seem to have an associated cost, it is often hidden in decreased user productivity caused by inadvertent deletion of important files, and the accumulation of all the time spent on the effort.

Migrate Files to Off-Line Storage

This is the traditional systems housecleaning, making copies to tape and then removing the files from the system. This removal of the files is often followed by a request from a user for the off-line material, with a good deal time and spent to track down the specific file. The archiving costs are combined with the costs of the recoveries and the lost productivity of users to make this an expensive solution.


HSM is an automated process which provides the best solution to the never ending demand for disk storage. By moving data to less expensive secondary storage, and recalling it automatically when needed, such that users receive the benefits of near-infinite disk storage without the cost.

Most HSM Systems have the following features:

Pre-Staging of inactive data to secondary storage

Some form of secondary storage is used. Typically this takes the form of a tape autoloader, optical juke box (Pinnacle Micro, or HP for example), a large tape drive or a combination of such devices. A key advantage of secondary storage is a cost per gigabyte in the range of tens of dollars for optical, and even less for DAT tape.The HSM system is responsible for moving copies of inactive files into secondary storage, in anticipation of the need to remove them from primary storage as the disk volumes fill. The data is pre-staged to avoid the performance burden of transfers of large data volumes during peak hours.

Monitoring of primary storage volumes with migration as needed

Throughout night and day the HSM system monitors the disk volumes it services. If the amount of data on the volume exceeds the configurable "high water mark" ( usually expressed as a percentage of total disk space), migration will occur. If pre-staging has been used, this migration requires nothing more than selecting the right files to migrate, shortening them to a very small "phantom" or "stub" file as a place holder, and stopping the migration when the "low water mark" is reached .

Automatic Recall

The users continue to see all data as on-line. When a file is accessed, a recall agent, resident in the client or on the server, initiates the process of moving the file from secondary storage back to primary storage.

DataSure Services believes that Hierarchical Storage Management has many benefits that can improve systems and human resource productivity.

For futrher information on host adapters, try our
Host Adapters Page
Host Adapters

ADIC Autoloaders and DLT
or our

Pinnacle Micro page
features information on their storage libraries, and our Pioneer Optical page
Pioneer CD-ROM and Optical Products
with information on their 500CD-R Jukebox, CD-Recordable page
CD-R page
has links to these and others, our Mass Storage Page
Mass Storage page
, and of course our


Thanks for visiting DataSure's HSM Pages.As the pages are developed we hope to leverage our expertise and cooperation from vendors to improve resources available to assist our clients in the development of proactive strategies, by providing a range of information and other resources allowing them to better evaluate available options, and enhance their competetive adavantages. This page was last updated
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DataSure Services is not connected with Datasure of Walnut Creek, California