Mass Storage (defined)

A Mass Storage Device can be defined as: Any device used to supply relatively inexpensive storage for large amounts of data. A sort of jukebox for optical disks or tape cartridges. A mass storage unit can automatically load any disc or tape in its library to provide quick access to vast quantities of information. (Computer Dictionary, Third Edition by Donald Spence, Camelot Publishing)

The text written for this paper will utilize several kilobytes of storage space. Several pictures are included in this paper. The pictures will utilize several hundred kilobytes of storage space. The finished paper will utilize about one megabyte of storage space - nearly an entire 3.5-inch floppy disk. But there is plenty of space on the hard drive. Or is there?

This picture (from: www.storage.ibm.com/storageadsmhome.htm) illustrates typical amounts of storage space used by common files.

Increased demand for storage space affects many people - from individuals (e.g. a Robert Morris College student) to corporations (e.g. USX). The solution for the student is an easy one. Purchase and install a larger hard drive. Or perhaps consider deleting those files from Speech Communications 2 class. The corporation will tackle this problem differently then the student will. One possible option is the use of Mass Storage.

Four types of Mass Storage technologies will be discussed: Hard Drives, Optical Disks, Tape Systems and the idea of HSM. The main idea all of these technologies is to end up with additional storage space - especially hard drive space.

Hard Drive Storage

Hard Drive Technologies could be compared to the hard drive of a personal computer or to floppy disks. Data and programs are stored on magnetic coated disks. Hard drives are fast, but they are expensive.

The capacity of hard drives is increasing. Computer Shopper magazine recently featured a 50 gigabyte hard drive. Additionally, the price of hard drive storage has been decreasing. But to continually purchase addition hard drive space may not be the most efficient business choice. Older files may hold great value. Deleting them to free up more space may not be an option.

Removable disk drives can be used to free up hard drive space. A Zip Drive can hold 250 megabytes of data. A Jazz Drive can hold up to 2 gigabytes. Storage can also be increased using RAID technology. RAID is the acronym for Redundant Array of Independent Disks. RAID is a storage device that can hold and control multiple hard drives. This technology also features protection against data loss.

Future trends for hard drives include increased data density of the disks and an increased spin rate. These two items translate into increased capacity and speed. Look for larger, faster hard drives soon. The cost per megabyte of hard drive storage will continue to decrease.

Optical Disk Storage

Optical disk technology includes CD-ROM, DVD, Magneto-Optical (MO) disk as well as Audio CDs. A laser is used to read/write data to and from these disks. Optical disks are not as fast as hard drives. But, they are cheaper to use and they feature a larger storage capacity. One problem with these disks is that today, many types are read-only.

Capacities: CD-ROM is 680 megabytes, DVD is 5 gigabytes and Removable MO disks are also 5 gigabytes.

These disks are for the most part removable. The writable types of disks can be used to store data and programs chosen by the user. Instead of the RAID technology employed by hard drives, optical disks can be used in an Auto-loader. An auto-loader is a jukebox-type device that holds multiple disks simultaneously. The capacity of an auto-loader is very large.

Future trends for optical disks include continuing decreases in prices of the disks and increasing the data density of disks. Larger disks coming soon.

Tape Storage

Tape technology could be considered a type of Snail vs. Hare technology. Tapes are slow. But they are very inexpensive and have a tremendous storage capacity.

A normal magnetic tape can hold up to 8 gigabytes of data. A DAT tape (Digital Audio Tape) can hold up to 24 gigabytes of data. The super star of the tape world is the DLT (Digital Linear Tape) with a capacity of 70 gigabytes. Tapes are also a very popular technology for baking-up programs or data.

Tapes also make use of auto-loaders. A diagram of one is shown below (from: www.byte.com )

HSM Technology

What if you could utilize the "Best of Both Worlds" when considering mass storage? The speed of hard disks along with the capacity and low cost of optical disks and tapes. A type of system using the different technologies is available today. It is called a Hierarchical Storage Management (HSM) system. The following (from: www.byte.com) gives an overview of an HSM system:

A hierarchical storage management (HSM) system is like a robot housekeeper for network storage. It monitors hard drives for not-recently-used files and migrates them to a storage medium that has greater capacity and costs less per megabyte.

Typically, storage media are in this hierarchy:

hard drive -- most expensive, fastest

optical -- less expensive, slower

tape -- least expensive, slowest

Robotic library systems manage both optical drives and tapes, so no manual

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