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 SCSI Disk
EIDE vs SCSI - Why purchase SCSI by P.A.P. Den Haan
Why use SCSI by Michael Neuffer
How to install SCSI Hard Drive by Rad
Determining Single-Ended SCSI or Differential (HVD) SCSI Interface by Paralan Corporation
SCSI - A game with many rules and no rulebook by Gary Field
SCSI Interface by David Risley
The Ten Commandments of SCSI by Gary Field
The Complete Guide to SCSI for the Powerbook by Charled Moore

Radified Guide to SCSI: Tutorial on to How to Install a SCSI hard drive

by Rad. It is taken from Radified.
Last updated: 15 Feb. 2003

This SCSI guide began with a group of friends who became interested in editing digital video. Disappointed with the performance of IDE drives at the time (especially as the timeline grew), we wondered if a SCSI hard drive would improve our editing experience .. and if so, how much.

I researched the subject, but found it impossible to find any consensus among enthusiasts in the PC community. Some hailed SCSI as the best thing since sliced bread, while others felt is was a complete waste of time and money.

I had a little extra cash on hand, so I decided to see for myself what all the SCSI hoopla was about. So I purchased an Ultra2-Wide SCSI controller (Tekram DC-390U2W), and the smallest (cheapest) 10Krpm SCSI hard drive I could find (9GB IBM Ultrastar 9LZX). I figured I could always sell the stuff if it turned out to be the waste of time that some had suggested.

After seeing what a difference (!) the SCSI boot drive made in my system, and how much more enjoyable editing video became, I transformed into a SCSI zealot overnight, recommending a snarling SCSI beast to those who wanted to give their systems the supercharged responsiveness of a SCSI-based workstation.

Hybrid Approach to Disk Storage

I advocate a hybrid approach to disk storage, which means that I recommend a combination of both SCSI & IDE/ATA drives. Specifically, I recommend a small, fast SCSI boot drive to run your:

  • Operating System(s)
  • Programs & Applications
  • Swap / Page File

... and a large IDE/ATA drive (or two) to complement your system with plenty of cheap mass storage. In this way you get the best of both worlds: the blazingly fast performance & responsiveness of a SCSI boot drive to run your operating system & applications, and plenty of disk storage from cheap IDE drives.

With this hybrid approach, you won't waste money by storing file archives on (relatively) expensive SCSI drives. Nor will your operating system and applications be limited by the (relatively) slow access times and spindle speeds (latency) associated with IDE drives and the single-tasking IDE interface.

The great SCSI vs IDE debate still rages in PC hardware forums all across the Net. It was no different back when I began researching storage solutions (~3 years ago). The optimal configuration seemed obvious. Yet back then, there were only two camps: SCSI elitists on one side, and IDE fascists on the other, and never the twain did meet. It surprised me that no one was advocating a combination of both.

To the best of my knowledge, I'm the first to advocate the hybrid approach to disk storage. Today, if you visit PC hardware forums, you'll find that the hybrid approach is now the dominant recommended disk storage solution for the performance-minded enthusiast .. certainly more so than the all-SCSI purists of yesteryear.

Since most people already have an IDE drive in their system, the addition of a SCSI drive produces an instant hybrid configuration. If someone is building anew system from scratch, they may, or may not, already have the IDE drive.

Note that this guide does not address the great SCSI vs IDE debate directly. Rather, my position is: SCSI *plus* IDE offers the best disk storage solution <for qualified users>. My system currently contains three IDE hard drives, so don't think that, because this is a SCSI guide, I'm here to bash IDE. I'm more pro-IDE than the staunchest IDE fascist. I contend that IDE drives have their place in every system.

The SCSI vs IDE debate can engage PC enthusiasts like few other techno-disputes. I do not wish to revisit this volatile topic. Here I merely try to present the facts, and provide ample references to support my claims. I leave the actual decision-making up to you, the reader .. to decide whether (or not) SCSI is right for you.

Before we jump into it, perhaps I should note that you can find this SCSI guide at any of these fine Radified URLs:

It has become surprisingly popular since being discovered by search engines. Try searching for SCSI guide in either Google or Yahoo, and you'll see what I mean. Before we begin, I want to take a minute to mention <shameless plug> a few other Radified guides that you might find helpful. For example:

Let's get busy. Without further introduction, I'll break with convention, get right to the point, and begin with my conclusion:

SCSI is not for everyone

Rather, SCSI is for the person who uses their PC in ways that take advantage of the benefits offered by the SCSI interface & SCSI components (more on this later), and who can afford it:currently ~US$250 for *both* a SCSI hard drive & SCSI adapter (even less if you know how to buy used equipment).

By the very fact that you're still reading, I assume (perhaps incorrectly) that you have the financial wherewithal to afford a SCSI hard drive & controller card, and that there's at least a possibility that you may be able to put a SCSI disk storage subsystem to good use.

Permit me to state the obvious and say that this guide is intended for people who can afford the cost of a SCSI drive and adapter card (less than the cost of a good 3D gaming graphics card) and who will put a SCSI-based system to good use. If you satisfy these qualifying criteria, I vigorously contend that your computing life will be much sweeter when running your O/S & apps from an enterprise-class (10- or 15Krpm) SCSI drive.

Wow Factor

If you're anything like me, you'll be surprised by how much snappier your system responds, powered by a snarling SCSI beast. It's no small difference. I saw a dramatic improvement .. after upgrading my previous boot drive (7200rpm IBM Deskstar) to a 10Krpm LVD SCSI drive, which is not even the fastest drive on the market).

The improvement I saw was comparable to upgrading to a Cable modem (from dial-up), or to installing my first 3D graphics accelerator card (Voodoo2). These are the only other PC upgrades that excited me enough to sit up and say, 'Whoa!'

Some people refer to this as wow factor. For me, upgrading my boot drive to an LVD-rated SCSI beast generated terrific wow factor. By contrast, my recent CPU upgrade - [from a C300a @464MHz to http://radified.com/Benches/cpuid_p3_700.htm] - left me comparatively disappointed (zero wow factor). From a seat-of-the-pants perspective, it felt as if my system responded three times faster with the SCSI boot drive .. based solely on the subjective feel of system usage both before and after the upgrade (not benchmarks).

The reasons why SCSI hard drives perform so much better than their IDE/ATA counterparts (at running your O/S & apps) get technical. I'll address them in greater detail later. But for now, the good thing is that you don't need to know all the über techno stuff in order to take advantage of the performance benefits offered by today's SCSI drives. The heart of configuring a SCSI components is found in SCSI IDs & termination, which is not rocket science.

Ultimate Disk Storage Config

It might be worth noting that, if we had an unlimited expense account, we could maximize the performance of our disk storage system by purchasing a *separate* SCSI drive to run each part of our system. In other words, we could dedicate one drive solely to run our operating system, another to run our applications, and a third for our swap/page file. Perhaps even a forth drive for our documents, if we really wanted to wax decadent.

Although this would improve our system's performance, it wouldn't be very practical. First of all, there's no such thing as an unlimited expense account. In the real world, everyone is interested in maximizing the performance bang for their hard-earned bucks. I'm sure you're no different. In this case, you should know that a single LVD-rated SCSI beast will provide the lion's share of performance enhancements offered by a SCSI hard drive and the SCSI interface.

This also might be a good place to note that SCSI is a true multitasking interface, while IDE/ATA is a single-tasking interface. Each device on an IDE channel needs total control of the bus in order to 'talk' (transfer data). SCSI, on the other hand, can have multiple 'conversations' occurring concurrently. More on this later.

Before going any further, perhaps I should note that SCSI is an acronym that stands for Small Computer System Interface. It's pronounced 'scuzzy'. The bus standard has been around for a while.

The Controller Card

Once you decide that SCSI is for you, the first item you'll need to consider is the SCSI adapter, which is also called the SCSI controller. You want to make sure that whatever SCSI adapter you select has the ability to run non-LVD devices (such as burners, scanners, CDROM & Zip drives) without degrading performance of devices running on the LVD channel (i.e. hard drives).

Mixing LVD (or U160) devices with non-LVD rated devices (on the same channel) will cause your LVD devices (hard drives) to run at non-LVD speeds (max 40MB/s, in what is called Single-Ended mode). Although you can run SCSI devices configured like this, this configuration is not optimal.

LVD is an acronym that stands for Low Voltage Differential. It offers performance enhancements that you definitely want in your system. Most notably, the ability to transfer data at rates of 80MB/s, or 160MB/s in the case of the Ultra160 protocol.

While adapter cards supporting nothing faster than the UltraWide (UW) protocol, which max's out at 40MB/s, are not necessarily a poor decision, I don't recommend them, for reasons I'll address later. Note that in each case, actual, real-life transfer rates will be somewhat less than the theoretical maximum, taking into account things such as 'bus overhead'.

In the case of Ultra 160, PCI bus limitations (133MB/s theoretical, 110MB/s realistic) also come into play (for 32-bit PCI slots). This means that today's 32-bit PCI bus is able to take *full* advantage of the U2W (80MB/s) interface, but not the U160 interface (160MB/s). This is not a major point, though If I were purchasing a card today, I would definitely buy an U160-capable card. But if cash is tight, you don't lose very much by opting for an U2W card.

I'm not sure if you can exceed the PCI limitation of 133MB/s when transferring data from one U160 drive to another, on the same channel (provided you have an U160-capable controller). I heard both yes & no. If someone knows for sure, let me know. This would only apply if your system contains two U160 hard drives, Again, not a major point.

A BIOS makes SCSI a Snap

Once upon a time, in the not too distant past, SCSI could be a bear (difficult) to install & configure. But with today's BIOS-sporting adapters, it has become surprisingly simple to configure your very own SCSI-powered workstation. Like I mentioned earlier, you'll need to become familiar with SCSI IDs & termination. But I promise that you won't find it very difficult.

You shouldn't take this to mean that you won't have a few quirks to iron out. Every system is different, each with its own issues. Working thru initial configuration glitches is considered a SCSI rite of passage. If you don't have any problems, it probably means that you did something wrong. =)

Everybody seems to have at least one initial configuration glitch that needs working thru. But I only know of *one* person who had so many problems that he gave up on SCSI entirely. And that was years ago, back when SCSI was much less user-friendly. The very act of expecting & anticipating initial-configuration problems seems to take the sting out of any problems you might actually have.

Either way, this guide will help flatten the daunting SCSI learning curve, and minimize your potential for problems. Fortunately for you, I've already encountered most of the problems you're likely come across on the path to configuring a full-blown SCSI-based system.

I've also received reports from many other SCSI users, who've shared their own problems, solutions, & tips, using a variety of system configurations, with a variety of SCSI drives & adapters. In the pages that follow, I address the common pitfalls in a straightforward manner, and steer you away from them.

SCSI with Windows XP

Update: 22jan2003 - Much debate has raged across the Net regarding the use of (fast) SCSI hard drives in concert with Windows XP: Microsoft's latest version of its market-dominating operating system. Since I am a big SCSI fan, I've been watching the debate and have avoided Windows XP, even though I like it a lot [still using Windows 2000].

Much has been learned by people far smarter than me. At the StorageReview, you can find the low-down on the situation. To save you some reading time [my eyes started burning halfway thru], I'll post a brief synopsis.

1. It's okay to install and run Windows XP from any SCSI drive.
2. You will experience slower file transfers [~ 50% slower] in WinXP when using Windows Explorer.

3. The reason for #2 above is because WinXP's Explorer transfers files in a more secure method [using something called a WRITE_THROUGH file flag].
4. The phenomena is only seen in SCSI drives cuz IDE drives [which most people use] don't include the WRITE_THROUGH flag in their command set. It's scheduled to be included at some later date.

5. Windows 2000 has a minor bug that ignores the WRITE_THROUGH command and writes the data to the (faster) cache instead of to the (slower) disk, even if the application asked it not to.
. You could lose data in Win2000 if you lose power while transferring a file. [I use the APC Back-ups 650.]

. This phenomena does not affect all file transfers in WinXP when using SCSI drives - only those that use the WRITE_THROUGH file flag [such as Windows Explorer].

If you want more info, StorageReview has one of the Net's better forums.

SCSI Nirvana

Note that you don't see any advertising here. So you don't have to be concerned about minced words, or parallaxed viewpoints. I try to tell it like I see it, and not make you read between the lines. Since I identify all of the common pitfalls, you have nothing but clear sailing into the blissful Shangri-La of true multitasking & blazing fast access times .. known as SCSI Nirvana. Discover for yourself why people get so excited about booting their systems from a snarling SCSI beast.

Best of all, you can now employ world-class technology - [designed primarily for the most powerful e-commerce servers, running full throttle, 24/7/365] - at a small fraction of what it would've cost only a few, short years ago. Never before has such robust storage performance been available at such reasonable cost.