From: David C. (shamino1@usa.net) Subject: Re: good SCSI card for Linux? View: Complete Thread (21 articles) Newsgroups: comp.os.linux.setup, comp.os.linux.hardware Date: 2000/01/20 Andrew E. Schulman writes: > Andrew E. Schulman wrote: >> >> I'm looking at SCSI cards and have a pretty good idea of features vs. >> price. One thing I don't know about is reliability. It's also >> unclear whether the cards come with suitable Linux drivers. Or do I >> need a SCSI driver for Linux? >> >> I wonder if anyone can recommend a SCSI card or brand that works well at >> a reasonable price, especially in light of any Linux experience. > > In particular: I see a Tekram DC390 Fast SCSI-2 controller for $45. > What do you think? Too cheap? It comes with a UnixWare 2.X driver. > Does that have anything to do with Linux? Your card is not likely to include a Linux driver. OTOH, your Linux distribution should include drivers for most of the popular SCSI cards. Check your distribution's hardware compatibility list. It will tell you what drivers are included. My own personal experience has been with Adaptec cards. I have two in my system: a 2940UW for the hard drive and a 1542B for the CD-ROM, Zip and tape drive. There were some driver glitches with the 2940UW (back in kernel 2.0.13), but they have been fixed in later releases (2.0.36 was fine, as is 2.2.13) I got my 2940UW for $160. This was a good price at the time (I've seen it for less, recently). I would not recommend a 1542 for fast devices (like hard drives) - ISA cards are slow. I have no first-hand knowledge of other brands. I would not dismiss a card merely because of a $45 price tag, though. Especially a "Fast SCSI-2" card. That card is conforming to an older standard that isn't terribly fast by today's standards. Just in case you don't know, here are the various SCSI standards and buzzwords you're likely to find: - SCSI - a generic term. Sometimes used to specify non-wide SCSI (see below.) - SCSI-1 - the original command-set protocol for SCSI. Only defined for hard drives. Other kinds of devices are non-standard under SCSI-1. You are not likely to find many SCSI-1 devices these days. SCSI-1 is sometimes used to refer to the large 50-pin Centronics connector used on some SCSI cables. This is incorrect usage of the term. SCSI-1 works on cables with all kinds of connectors (Centronics-50, micro-50, micro-68, etc.), although the Centronics-50 connector is the most common for these older devices. - SCSI-2 - an enhanced command-set. This one has definitions for more devices, including CD, and tape drives. SCSI-2 is sometimes used to refer to the micro-50-pin connector used on some SCSI cables. This is an incorrect usage of the term. SCSI-2 works on cables with all kinds of connectors (Centronics-50, micro-50, micro-68, etc.) - SCSI-3 - a command-set that defines even more features than SCSI-2. SCSI-3 is sometimes used to refer to the micro-68-pin connector used on some wide-SCSI cables. This is an incorrect usage of the term. SCSI-3 works on cables with all kinds of connectors (Centronics-50, micro-50, micro-68, etc.) - Wide - a variant on SCSI where data is transmitted 16 bits at a time over a 68-pin cable. Wide SCSI busses can support up to 15 devices (theoretically). Wide SCSI busses can move twice as much data, because they have twice as many data-wires in the cable. Wide SCSI is usually used in conjunction with Ultra, Ultra2 and Ultra3 busses these days. It is rare to find "fast-wide" devices today, although they do exist. Non-wide (sometimes called "narrow") SCSI busses transmit data 8 bits at a time over a 50-pin cable. Non-wide SCSI busses can support up to 7 devices. - Fast - The original SCSI spec only worked at relatively slow speeds (less than 3M/s for narrow devices, 6M/s for wide devices). The spec was soon changed to allow faster speeds (up to 10M/s for narrow devices, up to 20M/s for wide devices). Any non-Ultra card or device that supports more than 3M/s is usually said to be "fast". - Ultra - Ultra-SCSI doubles the data rate. The theoretical maximum speed for Ultra-SCSI is 20M/s. For Ultra-Wide SCSI, it's 40M/s. For backward compatibility, the bus (and devices) will run at Fast-SCSI speeds as necessary to support slower devices that are sharing the bus. (So to get the maximum speed, all devices on an Ultra bs should be Ultra.) Note that the Ultra's top speed of 40M/s is faster than most drives' capabilities. The benefit to the faster bus is so that multiple drives can use it simultaneously without slowing each other down. - Differential - Normally, each signal-carrying wire of a SCSI cable is twisted with a ground wire, for sheilding. With differential SCSI, it is twisted with a wire carrying an electrically-opposite signal. This greatly reduces the effects of EMI and allows for longer cables. Non-differential busses are known as "single-ended". Note that differential and single-ended devices can not coexist on a single bus. - LVD - Low Voltage Differential - The original differential SCSI spec used a higher voltage than single-ended SCSI. LVD uses the same voltage as single-ended SCSI. The maximum length of an LVD bus is 12m. (The mximum length of a high-voltage differential bus is 24m.) This is a great improvement over earlier standards. (The maximum length for Fast- and Fast-Wide SCSI is 6m; Ultra is 3m and Ultra-wide is 1.5m.) - Ultra2 - doubles the speed of Ultra SCSI to 40M/s for narrow busses and 80Ms for wide busses. Ultra2 devices are LVD. For backward compatibility, the bus (and devices) will run at Ultra- or Fast-SCSI speeds as necessary to support slower devices that are sharing the bus. If a non-LVD device is attached to the bus, all Ultra2 devices will fall back to a non-LVD protocol. (So to get the maximum speed, all devices on an Ultra2 bus should be Ultra2). Note that the Ultra2's top speed of 80M/s is faster than most drives' capabilities. The benefit to the faster bus is so that multiple drives can use it simultaneously without slowing each other down. - Ultra3 - sometimes known as Ultra-160 - doubles the speed of Ultra2 to 80M/s for narrow busses and 160M/s for wide busses. Ultra3 devices are LVD. For backward compatibility, the bus (and devices) will run at Ultra2-, Ultra- or Fast-SCSI speeds as necessary to support slower devices that are sharing the bus. (So to get the maximum speed, all devices on the bus should be Ultra3.) Internal Ultra3 busses require a ribbon cable where the differential wire pairs are twisted together. A straight ribbon cable won't work. (The twisted-pair ribbon improves performance of Ultra2 as well, but it's not required there.) Note that the Ultra3's top speed of 160M/s is faster than most drives' capabilities. The benefit to the faster bus is so that multiple drives can use it simultaneously without slowing each other down. As for UnixWare, that driver is meaningless. UnixWare was (still is?) a UNIX OS sold by Novell. Its drivers will not be compatible with Linux. -- David