Talk:SCSI

Fiber Channel is not an alternative spelling of Fibre Channel.

Pleonasm?

"SCSI is pronounced "scuzzy" when spoken aloud"... Isn't this a bit pleonastic? --Edcolins 11:51, Oct 28, 2004 (UTC)

"while occasional attempts to promulgate the more flattering pronunciation "sexy" have never succeeded." Nowadays we're trying to get it to be pronounced "sucksy" ;) --148.84.19.92 15:25, 9 Mar 2005 (UTC)

IDE?

The article says that PATAPI is SCSI over IDE. Isn't this a misnomer? As I recall, parallel ATA is not the only form of IDE, though PATAPI is, of course, over parallel ata.

Not quite; something the article doesn't make clear is that SCSI is a command set as much as (and, now even more than) it is an interface. If you look at the official specs for ATAPI, it is indeed sending SCSI commands over the ATA bus; in fact, most ATAPI devices these days are actually SCSI devices that speak enough ATA to get by. -lee 07:11, 13 Jun 2005 (UTC)

spice up SCSI

good article, Mac users in particular grew up on SCSI and SCSI peripherals

How about some pics of the typical fat cables and giant terminators that people remember:

http://images.google.com/images?q=scsi&hl=en&lr=&sa=N&tab=wi

Also what about the SCSI logo ?

http://images.google.com/images?hl=en&lr=&q=scsi+logo&btnG=Search

I agree that this article needs some pictures. Anyone willing to take some? 203.208.80.13 00:51, 14 September 2005 (UTC)[reply]

SCSI protocol

This article only seems to talk about devices...as far as I know, in the Linux kernel (for 2.6 at least), firewire IEEE1394 / USB storage devices / Ipod's, etc. they also use the SCSI protocol to communicate to the kernel. Any elaboration on this? -- Natalinasmpf 02:27, 19 Apr 2005 (UTC)

You are correct; most of this article focuses on what is now officially referred to as the SCSI Parallel Interface, which is just one part of SCSI-3 and has little to do now with the SCSI command set (which is, as you and others have noted, is implemented on things that are about as far from SPI as you can get). At some point (not tonight, since it's late) I'll go through and sort things out. -lee 07:05, 13 Jun 2005 (UTC)

June 22, 2005:

The article should mention "packetized" SCSI that was introduced with Ultra-320. IBM preferred the term "information units" over "packets". I think this was around 2002 or early 2003.

Also, the "Ultra" designations were promoted by the SCSI Trade Association but not used in the ANSI standards. After SCSI-2, the physical interface standard was separated from the logical layers, and became SPI (for SCSI Parallel Interface) and went through generations SPI-1, SPI-2, SPI-3, SPI-4 and SPI-5. STA wanted marketing-oriented nomenclature that reflected the actual maximum data transfer rate of the bus. Note that the SPI acronym can easily cause confusion with other standards.

I don't think "All SCSI standards have been modular, defining various capabilities which manufacturers can include or not" is true of SCSI-1 or SCSI-2, which were monolithic specifications, unless "modular" means something different from what I take it to mean.

I didn't write that part. But certainly SCSI-2 has wide scope for variation in device capabilities, with all sorts of contexts in which initiator and target are supposed to negotiate for a set of common capabilities.

I think this is too opinionated for the article, but to my mind one of the weaknesses of SCSI is that it is a humongous specification--SCSI-2 is about an inch thick--and it is very easy for devices to fail to implement some portions of it correctly. Obviously, if an Adaptec card doesn't work properly with Seagate disks they'll catch it and fix it, but obscure corners of the specification can be ignored, resulting in SCSI cards that work with most but not all devices, and vice versa.

It is similar to problems encountered with TIFF in, say, the early nineties, when it was quite possible to have a TIFF file that completely conformed to the TIFF spec but which could not be opened by PageMaker.

Another problem, to my way of thinking, is that the safety margins on things like cable length appear not to be conservative enough. I notice that Adaptec consistently specifies maximum cable lengths that are exactly half those allowed by the spec! And, worse yet, in the real world, if you have a cable configuration that theoretically should work, but the terminations are slightly bollixed, or there are slight impedance mismatches where cables join at connectors, the result is subtle and sometimes intermittent problems, rather than obvious failures.

Yeah, one big issue with multi-drop cables is for devices in the middle (or anywhere not at the ends) of the cable. They would be much more susceptible to reflections on the received signals, and also have the burden of driving two cable segments and not just one, so they would produce about half the signal strength on the incident wave that a device on the end of the cable would.

Vendors try to solve these problems by building in automagic self-configurating features, which help when they work and make things worse when they don't. For a while we had an issue with Adaptec cards, when they first introduced a feature they called "domain validation." This meant that instead of trusting what the device said its capabilities were, the card would dynamically test for certain device characteristics and capabilities. Our device would sit there and say "I'm synchronous, I'm synchronous, please please run synchronous so we can get the data transfer rates we need" and for some reason the card would say "Nyaah, nyaah, I don't BELEEEEVE you, say what you like, I'm going to run asynchronous anyway" making our stuff basically not work unless the end-user turned off domain validation. This is no longer true, but we never found out exactly what had changed about their "domain validation" process. Dpbsmith (talk) 19:21, 22 Jun 2005 (UTC)

Termination

The description of the termination network is inside out and backwards. Passive termination uses 2 resisters to TermPwr and ground. Active termination uses 1 resistor to a regulated 3.3 volt source. Differential is 2 lines that are each terminated. In single ended, the other line is a ground. The active termination uses less power and therefore uses a smaller resistance that more closely matches the cable impedance. The tutorial that is already link to has it right <http://www.scsita.org/aboutscsi/SCSI_Termination_Tutorial.html>. It should also be mentioned that the term power fuses have mostly been replaced by a current limiting device. ~ Dan Oetting 136.177.111.33 00:32, 5 November 2005 (UTC)[reply]

Thanks. I got that wrong so I have now corrected it. neilm48, 5 November 2005.

What's used now?

It's been a long time since I used SCSI. What is used now in servers? Isn't some form of IDE used now? --Gbleem 16:13, 8 November 2005 (UTC)[reply]

Newbie Question

In a read or write command block is the data transfer length in bytes or LBAs?

JimT

Connectors

I miss the description of various SCSI connectors.

xerces8 --213.253.102.145 12:31, 16 January 2006 (UTC)[reply]