Solving The Nee d To Forage For Storage The process of changing discs operates under software control. Timing disc exchanges, monitoring the status of drives and tracking the data residing on discs is a complex process. Many vendors of optical disc changers supply only low-level drivers, and the software that controls the higher-level tasks are part of the data management application. Be sure to select a changer that's compatible with your data management software. The use of optical disc changers often involves networks, but rarely does the changer connect directly to the network. Generally, the optical disc changer attaches to a host computer or server, which in turn connects to the network. Most changers communicate with their host computer through a SCSI -2 interface. In addition, many optical disc changers have an interface that controls the robotics. Optical disc changers usually attach to a network server, but may be used with mainframes or desktop computers. Making the Right Choice Several differentiating factors drive the selection of an optical disc changer. The competing products differ considerably in capacity, performance, reliability and cost. Following is a list of features buyers should compare when evaluating products. · Compatibility. As organizations build their data-storage infrastructure, issues of software applications and computing platforms generally will be addressed first. The selection of components such as optical disc changers will be limited by compatibility with the primary computing environment. Further, the software that controls the optical disc changer will be selected prior to the selection of the hardware. · Capacity. Carefully consider your organization's volume of data and t he way it manages that data. If, for example, optical media functions mainly as an archive, then the ability to rewrite discs is not critical. To assess the overall volume of data an optical disc changer can handle, consider the total number of disc slots multip lied by the capacity per disc. The efficiency of large-capacity systems will be greatly diminished if the unit cannot accommodate the number of simultaneous users who require access. · Support. Unlike most other computer equipment, optical disc changers rely on moving mechanical parts. Repairs require a specialized technician, and self repair often invalidates the warranty, so plan to pay for ongoing support. Some vendors let customers perform tasks such as installing additional drives and upgrading ROM. · Costs. Although optical media offers a low cost per megabyte, the costs increase dramatically when you factor in the price of an optical disc changer and its maintenance. Be sure to compare overall costs for an o ptical media-based approach with an alternative based on magnetic discs. CD-ROM Network Servers While optical disc changers offer the ability to manage user-recordable data, CD-ROM network servers specialize in providing network access to data prerecorded on CD-ROM discs. CD-ROM reigns as the preferred medium for data distribution and increasingly is being used as the installation medium for software. One copy of data, spanning multiple discs, may be shared by users throughout the organization's network. Architectural Models Choosing the right CD-ROM network server can be a daunting task, especially given the complexity and variety of network operating systems and media types. These products can be organized into several categories by architectural approach. · Optical Server/Redirector. One CD-ROM networking method involves the use of a dedicated DOS-based server that requires a redirector module on the client computer. Client computers load the CD-ROM redirector in a ddition to the other shells or requesters needed for network access. The CD-ROM server under this model is an Intel-based server with a fast processor, a large amount of memory and a set of CD-ROM drives connected through a SCSI-2 interface. The server will boot up under MS-D OS and then load the CD-ROM server operating software. The main weakness of this model lies in its use of DOS rather than an advanced multiprocessing operating environment, such as NT, NetWare or Unix. But this approach does offer a high degree of compatibility--the same server usually can be configured to support NetWare, NetBIOS and/or TCP/IP networks.

Updated March 25, 1997