The Book of SCSI, 2nd Edition

Craig Maloney contributes the below review of a book he claims is long overdue -- the second edition of Gary Feld's The Book of SCSI. Probably it won't be long until someone is reviewing The Book of Firewire, but SCSI remains probably the most widespread standard for high-quality, reasonably priced storage. I know it's gotten better since the last time I struggled with termination issues and bad cables, but if you rely on SCSI every day, you may need this book.

The Book of SCSI, 2nd Edition: I/O for the New Millennium author Gary Field, Peter M. Ridge pages 456 publisher No Starch Press rating 7.5 reviewer Craig Maloney ISBN 1-886411-10-7 summary A one stop resource for the SCSI protocol.

What's Good? For those in a hurry, Appendix A (The All-Platform Technical Reference) is the entire book in a nutshell. I think Appendix A should be included with every SCSI card sold. It includes pin-out descriptions of the major and not-so-major SCSI interfaces, tables for bus timings, and a quick description of termination rules. The pages that surround Appendix A are also quite good.

The chapter on connecting devices to a PC talks at length about one of the more troubling aspects of SCSI; termination. Anyone who has had to troubleshoot SCSI installation problems will enjoy how thorough Chapter 6 deals with troubleshooting. (It even includes what a SCSI signal should look like on an oscilloscope). Programmers will find a Chapter with information on programming using ASPI, as well as protocol specifications for those looking for more low-level information. You'd be very hard pressed to find a more complete and readable treatment of the SCSI protocol than this book.

What's Bad? Unfortunately completeness can lead to information overload. Novice users will find themselves at a disadvantage with the sheer amount of material presented.

When discussing how to set up a SCSI adapter, the book mentions the various PC busses from the earliest IBM PC to draft revisions of PCI and everything in-between. Had I been a novice reader, I would have been overwhelmed with all the information about historical PC busses that are no longer in use. (When was the last time you used VLB or EISA?) In the interest of completeness, the authors also include a chart comparing these interfaces. I question whether this is really necessary. Some may also be put off by the hand-drawn diagrams in the earlier chapters.

On the CD

The CD includes items such as the SCSI FAQ, ASPI Development Files, ASPI tar, SCSI disk driver source for MSDOS, Western Digital SCSI Utilities, SCSITool, Postmark I/O benchmark source code, and Linux SCSI information. Of note, the CD also includes a PDF file of the entire book.

What's in it for me?

The Book of SCSI is definitely written by SCSI enthusiasts. On the early pages, the authors include a bit of SCSI poetry, and the CD includes a text file entitled "SCSI: A Game With Many Rules and No Rulebook?". This book reads with an excitement only an enthusiast can project. If you have ever been curious about SCSI, I encourage you to sit down and read the first few chapters of this book. If you are in a position to use SCSI components more than occasionally, I recommend you purchase this book and keep it on your reference shelf for those times when troubleshooting is necessary.

My biggest complaint? I wish the authors had written this book ten years ago. However, it is still a welcome addition to my library today.

• Chapter Listing
• Chapter 1: Welcome to SCSI
• Chapter 1.5: A Cornucopia of SCSI Devices
• Chapter 2: A Look at SCSI-3
• Chapter 3: SCSI Anatomy
• Chapter 4: Adding SCSI to Your PC
• Chapter 5: How to Connect Your SCSI Hardware
• Chapter 6: Troubleshooting Your SCSI Installation
• Chapter 7: How the Bus Works
• Chapter 8: Understanding Device Drivers
• Chapter 9: Performance Tuning Your SCSI Subsystem
• Chapter 10: RAID: redundant Array of Independent Disks
• Chapter 11: A Profile of ASPI Programming
• Chapter 12: The Future of SCSI and Storage in General
• Appendix A: All-Platform Technical Reference
• Appendix B: PC Technical Reference
• Appendix C: A Look at SCSI Test Equipment
• Appendix D: ATA/IDE versus SCSI
• Appendix E: A Small ASPI Demo Application
• Glossary
• Index

You can purchase this book at Fatbrain.

Comments

Termination

[Carl Drougge]

What's so difficult about termination anyway? Terminate both ends of the bus, nothing else. If you have both internal and external devices, check if your controlles uses the same or separate buses for them. That seems to be it to me..

Re:Termination

[Anonymous Coward]

I do not think that termination is a reason for the decline of SCSI on the consumer market. I think cost is. Most users do not understand the benefits of SCSI. Most users also do not understand that SCSI under Windows 9X/ME is simply useless, and find its performance lackluster because of the lack of OS support.

Termination has if anything, gotten simpler over the past few years. Devices other than mass storage wide devices are becoming rarer. Few devices other than tape still ship in narror formats.

Most current HBAs for SCSI cards do an excellent job of auto-termination. With most new SCSI cables shipping with built in multi-mode terminators, the job is even simpler. Removing terminators from LVD devices also simplified the matter.

There are some instances of designers incorrectly implementing auto-termination schemes, and bus widths, but all in all, a good designer can get it right. The only complexity comes when people do not read documentation. Serialized busses such as SATA and serial SCSI will make life even easier going forward, as all points will require termination.

I love SCSI!

[aussersterne]

IDE is clumsy and slow compared to SCSI when you start to get many devices in the same machine.

I have a 3-channel LVD SCSI controller in my video system and it's talking to devices of all vintages:

1) Three 18.2GB Barracuda LVD drives in a RAID-0.
2) Four 9.1GB Micropolis UW drives in a RAID-0.
3) 8x CD-R (not CD-RW) drive.
4) Brand new DVD-R drive (whoopee!)
5) Two 1.3GB 5.25" Magneto-Optical drives.
6) 7/14GB 8mm tape drive.
7) 12/24GB 4mm tape drive.
8) Very old (but needed) Archive 2150S (QIC-150).
9) 100 MB Zip drive.
10) 300 DPI scanner (for rough stuff).
11) 1200 DPI scanner (for more important stuff).

The system lives in a server case with dual 450W power supplies, so of these devices, only the two optical drives and the two scanners are external. There are only three cables inside the case for the lot. Theoretically, there are 28 more SCSI IDs available for use.

Now, the nice thing about this is that I can have damn near all of them running at the same time without any appreciable slowdown -- something that never happens on my "play" system with IDE drives.

On my IDE system, I've got two hard drives, a CD-RW and an IDE tape, and the IDE channels often seem to slow each other down and fight for control when I start to burn, backup, and do lots of disk I/O at the same time. I've been told that this is because a single IDE interface doesn't do concurrent access to both drives.

Either way, I love using the SCSI system. It's an I/O monster. And I love being able to just hang whatever kind of device I need to use off of the external connector and know with reasonable certainty that Linux will support it. Long live SCSI.

Re:Since when was SCSI reasonably priced?

[Jeffrey Baker]

People buy SCSI drives for their performance. It is true that you can buy a SCSI device and an IDE device with equal performance. But, the highest performance SCSI device is a lot faster than the highest performance IDE device. In fact, a high-end SCSI device from 5 years ago is likely to beat any IDE device you can buy today.

For example, the tired old Seagate Cheetah 4LP, introduced in 1996, is still faster than the fastest IDE disk you can buy today, the WD800BB. The Cheetah delivers 50% more performance in the IOMeter file server benchmark (2.21 MB/s vs. 1.40 MB/s), responding on average 700ms before the WD does.

SCSI over IP... what about IP over SCSI?

[Eg0r]

The project's home is here but hasn't been updated in a lonnnng time.

Basically, take 2 computers with a scsi card in each, and use a scsi cable to connect the two machines. I don't know how this solution compares to myrinet or gigabit ethernet in terms of performance, but the idea is a nice one.

Re:3ware RAID cards vs SCSI

[Anonymous Coward]

Hi Sid:

I'm in the process of having a file server built for myself using similar technology. It is not built (and thus is not in my hot little hands) so I cannot speak from experience. You might be interested in the data at Storage Review . Although Storage Review focuses on timings under a Microsoft O/S, the IOMeter measures are interesting, and they have a nice database of measures that allows you to query for a comparison.

One interesting note is that 3Ware's 7400 series appears (according to their analysis) to be weak at Raid 5 performance (I've decided not to go Raid 5 so it is not currently an issue for me). If you need Raid 5, you might want to consider an Adaptec 2400 series which allows you to plug in extra cache memory on the card for write buffering.

The FreeBSD mailing lists have recently had some tales of woe for a Raid install. One speculation is that the IDE drives don't have staggered spin up like their SCSI counterparts, so if you have a large number of drives, you may need extra power to get the system to startup reliably (get a redundant or high capacity supply and offload some drives perhaps).