Solving The Nee d To Forage For Storage · NetWare volume emulation. This approach makes CD-ROM discs on the server appear as NetWare volumes. The same shell or redirector used for NetWare server volumes also works for CD-ROMs. The CD-ROM network server under this model usually is a NetWare server with a set of CD-ROM drives attached via a SCSI-2 interface. This server may also be used for file and print services. Combining the CD-ROM server with an existing NetWare server offers some savings, but may reduce performance by taxing the memory resources available for data caching and by increasing the volume of data traffic the server must support. · Windows NT services. As Windows NT gains ground, some products that offer CD-ROM ser vices in this environment are reaching the market. NT offers built-in capability to share CD-ROMs to network users. Add-in products offer specialized CD-ROM management capabilities, increased performance and tools to make it easier for users to access CD-ROM data. A typical server includes an Intel-based microcomputer and a set of CD-ROM drives attached via a SCSI-2 interface, and it runs Windows NT Advanced Server. · CD-ROM miniservers. Recently, products have emerged that use specialized diskless hardware to share CD-ROMs. These devices are not full-blown servers: They lack keyboards, monitors, disk systems and printer ports. The devices do contain an embedded SCSI controller, a network connection, a microprocessor and internal memory for holding configuration information and for buffering or caching CD-ROM data. All run some proprietary operating system optimized for its specialized function rather than a general-purpose network operating system. A CD-ROM miniserver makes its associated CD-ROM drives appear on the network in a variety of ways. Some allow CD-ROMs to appear as NetWare volumes, as NT services or as a mountable Network File System (NFS). Capacity and Performance CD-ROM network servers vary tremendously in capacity. T he basic issue involves the number of drives you can connect to the server. Avoid the limitations of the original SCSI architecture in favor of devices that use SCSI-2 or other SCSI extender technologies. Performance also is a major consideration. CD-ROM drives with an average response time of about 100 milliseconds (ms) are quite sluggish when compared with the 8-ms to 12-ms response of magnetic drives. With the current generation of 12X drives, the sustained data throughput approaches that of magnetic media. CD-ROM network servers compensate for the inherent slowness of CD-ROMs through several performance-enhancing technologies. Techniques such as read-ahead, SCSI disconnect, data caching to magnetic disk and caching to memory can be implemente d so that networked CD-ROMs outperform standalone drives. When configuring a CD-ROM network server, balance capacity and performance. As you increase the number of CD-ROM drives, you need to add more memory and faster processors. A popular strategy offered by some CD-ROM network servers involves transferring data from the CD-ROMs to magnetic disks. With the rapidly decreasing costs of magnetic storage, it is often cost effective to purchase a few 9-GB magnetic drives rather than the number of CD-ROM drives that would be required to offer the same amount of data. This strategy also can offer a tenfold increase in performance. The downside is an increase in the complexity of managing the server and the amount of time required to transfer the data from CD-ROMs. Hardware Options When selecting a CD-ROM network server, examine all components for quality and performance. These products may or may not come with CD-ROM drives installed. In the rapidly evolving CD-ROM drive market, purchasing d rives a la carte may let you find faster equipment. The amount of memory installed makes a marked difference in performance. Raw access to the CD-ROM drives takes about 150 ms, while access to memory is practically instantaneous. Caching CD-ROM data to memory boosts performance by taking advantage of the likelihood that the same data will be requested multiple times. Only the first request requires access to the CD-ROM drive while subsequent requests for the same data can be serviced from memory cache. Adding more memory increases the chances that data requests can be satisfied without accessing the CD-ROM drive. A fast processor will also boost system performance. For NetWare- and NT-based servers, choose the fastest Pentium available. It is harder to evaluate the processor embedded in the CD-ROM miniservers, since many use proprietary processors and architectures. With CD-ROM miniservers, you also must look at the speed of the processor and the amount of memory installed. With these diskless devic es, the amount of flash memory also is important, since it must hold the OS and configuration information. Look for CD-ROM miniservers that have OSes that can be upgraded with software rather by replacing ROM chips.

Updated March 25, 1997