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Hierarchical storage management (HSM) organizes data into tiers for cost and space efficiency. Frequently used data is stored on faster drives and moved down as usage decreases. HSM software catalogs and manages requests, with various features available. Retrieving less-used data can take time, but packing small files into archives can help.
Hierarchical storage management (HSM) provides organizations with a means to organize data archiving and retrieval into separate tiers for cost management and storage space efficiency. The technique is also sometimes called layered archiving. It works similar to a cache, but on a much larger scale, where frequently used data is stored on faster disk drives up front and stored on slower media at lower levels. Because some files are used more often, they reside in the top tier and are then moved down tiers when they are no longer in use.
The backbone of hierarchical storage management is software. A very detailed logic is needed to catalog the data and control frequently used files which should reside at the top level. The software is also responsible for managing requests at the library level and ensuring that these requests are made in a timely manner.
There are many different features available for various hierarchical storage management software implementations. Some software may allow for a backup level, where all data, whether it is frequently used or in archive, is also sent to additional long-term storage media. Other features may include integration with computer systems using the HSM. Here, data is pulled from other servers or workstations on the network to the main HSM and further organized down to the disk or archive level or a full backup.
Implementations of hierarchical storage management can also vary based on the use case. In some situations, a portion of a large file will reside on a high-speed disk and be linked to the rest of the file on the storage medium. When a user request arrives, the first part of the file is read from disk, while the rest is retrieved from the storage medium. This technique is often used in large streaming media implementations, such as Internet video.
There are also some disadvantages of hierarchical storage management. Specifically, it is the time required to retrieve less often used data from the storage tier. In the case of many small files, for example, it can take hours or even days for the robotics to pull together the request which can be spread across multiple discs in the jukebox. In these cases, system administrators typically recommend that you pack large quantities of smaller files into single archive format files. The archive tier then only needs to search for a single file, usually stored on a single medium in the library.
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