Ask The SCSI Expert.Visit the SCSI SCSI in full Small Computer System Interface Once common standard for connecting peripheral devices (disks, modems, printers, etc.) to small and medium-sized computers. SCSI has given way to faster standards, such as Firewire and USB. Trade Association's web site (www.scsita.org) to ask the SCSI Expert a question. Q: Is it possible to allow two computers to share SCSI devices? I would like two computers to be able to read and write to the same hard drive and CD-ROM drive A device that holds and reads CD-ROM discs. CD-ROM drives generally also play audio CD discs by sending analog sound to the sound card via a 4-pin cable. For specifications of 10x, 20x, etc. drives, see CD-ROM drives. See CD-ROM, CD-ROM changer, CD-ROM server and CD-ROM audio cable. . I realize that this could be done by networking or by other methods, but I was curious if SCSI could accomplish this. I need availability without rebooting, though not necessarily the ability to read/write at the same time. For example, a switched solution would work if both systems recognized the shared devices without reboots, but only one had them available at any given moment. A: Sharing a SCSI bus is fairly straightforward at the hardware level. As usual, you will need to ensure that the SCSI Ids are all unique. Sharing at the software level is not so easy. Operating systems Operating systems can be categorized by technology, ownership, licensing, working state, usage, and by many other characteristics. In practice, many of these groupings may overlap. (including Linux) have file management software that is written with the assumption that they are the only entity updating the file system. If two file managers access the same disk at the same time, file structures get corrupted. Even if one system only reads files, it can get confused because it might cache a structure that the other system updates. If both systems only read (as would be the case with a CD-ROM CD-ROM: see compact disc. CD-ROM in full compact disc read-only memory Type of computer storage medium that is read optically (e.g., by a laser). ), then sharing is possible. NFS (Network File System) The file sharing protocol in a Unix network. This de facto Unix standard, which is widely known as a "distributed file system," was developed by Sun. See file sharing protocol and WebNFS. NFS - Network File System and other networked file sharing protocols get around this problem by talking to Noun 1. talking to - a lengthy rebuke; "a good lecture was my father's idea of discipline"; "the teacher gave him a talking to" lecture, speech rebuke, reprehension, reprimand, reproof, reproval - an act or expression of criticism and censure; "he had to the remote system's file manager and not directly to the disk drive. Thus, only one file manager accesses a file system at a time. There is an early standards effort at using SCSI in a networked fashion called SCSI Secure Sockets (SSS SSS abbr. sick sinus syndrome ). This very early draft standard is available at ftp.symbios.com/pub/standards/io/t10/drafts/sss/sss-r00.pdf. Q: The SCSI terminology page defines a maximum cable length for a SCSI interface running at maximum speed: Do you have the maximum length for an interface that is running at some other speed? For example, what would be the maximum length for a Fast SCSI interface running at 4.445MB/sec? A: The cable distance has more to do with the round trip time of the cable and the loading on the cable. Enhanced Parallel Interface (EPI EPI exocrine pancreatic insufficiency. ) technical report reviews the issues of cable length. Thirty meters is possible with Teflon cable and very low loading from the devices. You can view the EPI technical report at http://www.symbios.com/t10. Q: What is the difference between active and passive termination on a SCSI bus? Why would you choose one over the other? What happens to the SCSI bus when each type of termination is implemented? A: Active termination is required for the higher speed operations and will make some systems work that will not work with passive termination. For example, on any hard disk or Jaz drive, you should always use active termination. Passive termination is used on slower equipment. If you mix the termination on the bus, it will work, but may give data errors at the higher speeds. Active termination provides higher pull up current and a better impedance match; the characteristics do not change will termpower fluctuations. Q: Could you point me to a graph or data showing the SCSI 3.5-inch HDD (Hard Disk Drive) See hard disk and HDD caddy. HDD - hard disk drive maximum size estimates for the next year or two? I'm seeing 50GB now on the Seagate web site. A: It follows Moore's Law "The number of transistors and resistors on a chip doubles every 18 months." By Intel co-founder Gordon Moore regarding the pace of semiconductor technology. He made this famous comment in 1965 when there were approximately 60 devices on a chip. of doubling every 18 months. In 2001, you can expect 72/100GB disks. Around 2003, you can expect 144/200GB disks. And before 2005, expect 244/400GB disks. |
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