SCSI hard drives

Factual Questions
1

I’d really like to get a new hard drive, but I have a SCSI interface, which means
a) There’s very little selection
b) They’re very expensive

I saw an eight gigabyte hard drive for $250, but I really don’t want to pay that much for such a small drive. Are there any drives that will work with a SCSI interface that are cheaper?

2

TheRyan, I’d personally recommend that you purchase a Promise Technologies IDE card and start using IDE drives. IMO, newer IDE drives are cheaper, just as fast, if not faster than SCSI(depending on how old your SCSI system is), and at least as accurate.

If you had a SCSI RAID system, Promise offers a IDE RAID card for like 60-80$

Other than that, I’d get used to purcahsing disgustingly expensive SCSI drives…

-Sam

3

The Ryan…

What kind of environment will your drive be used in? SCSI drives are ideally suited for server/extreme disk-intensive situations. IDE drives are nice and cheap because they use the CPU to handle all the I/O. SCSI controllers offload this overhead from the CPU, and the drives themselves contain the intelligence to cut down on this overhead even more.

This is extremely simplified, but the gist of it is that SCSI drives are only really needed for environments where drives are working 24/7. For normal home-system usage, while scsi drives are indeed faster, it’s not really noticed. Sure, napster loads a half-second faster, but so what.

IDE is a sloppy hack interface, but it works for home systems.

4

One more thing… You said you have a scsi controller… but just about every motherboard has an onboard IDE controller… If its of recent vintage I’m sure it has at least a UDMA 66 interface, which, again, should be perfectly suitable for a home PC.

5

Be aware that with a mix of EIDE and SCSI HDDs, the system will want to boot from the EIDE drive. Not a problem if you’ve already got an EIDE drive, but possibly a problem when adding an EIDE drive to a system operating with SCSI drive(s).

6

Well, I notice it sometimes. If you’re an avid computer game player like myself you see the effect of EIDE drive vs. SCSI frequently while playing. Some games will load or swap gamedata to the drive during gameplay which causes the game to ‘hiccup’. Let me tell you this can be quite annoying when the Zerg Overlord is bearing down on you!

That said IDE drives are just fine (even for gameplaying) so unless you have a server class machine (as has been mentioned) the money spent on SCSI just isn’t worth it. Zuma also brings up a good point that 99% of all motherboards have an IDE controller already built on to them. Chances are your CD drive is plugged in to one (although you may have a SCSI CD as well). The IDE controller will accept two devices and many motherboards these days have a secondary IDE controller as well allowing for a total of four IDE devices in your system.

7

Staples has a deal this week only where they’ll throw in a
ATA/66 PCI EIDE card for free with a 60 or 7200 RPM 40 gig Maxtor Drive purchase (drive at reg price of 240 or so). Not a bad deal frankly. I got one of these drives (40 gig unit) and they are spectacular!

As noted previously except for special purpose apps EIDE yields much better bang for the buck. Lets see 8 gigs vs 40 gigs for the same price and performance?

See http://www.storagereview.com for head to head IDE and SCSI drive comparisons. It’s a great site for accurate drive data.

8

This is for a home system. I usually leave my computer on all day, but I don’t think that’s what zuma meant by “working” 24/7.

beatle: can I just move config.sys and autoexec.bat to the new drive? Or do I have to move the entire OS over?

How do I check if I have an IDE controller? Go to Control Panel or something? Or am I going to have to open up the tower and physically look? Or call up the manufacturer?

9

First off, I dare someone to compare, in Human time, the difference between a SCSI-ultra HDD and the speed of an ATA66 7200RPM drive in a competent sytem. Your game will swap exactly the same with an EIDE/66 drive as it will with a SCSI drive if they are configured the same.

The only improvement would be if it was a brand new SCSI interface(like HP’s "Superfast 10,000rpm Ultra 160 SCSI hard disk drive with Ultra 160 SCSI controller on-board; Ultra2 SCSI controller optional "), which, AFAIK is the fastest SCSI interface around.

Now, The Ryan, was SCSI added to your computer after you got it? or was is standard config that way? Is the motherboard a SCSI motherboard?

Look at the motherboard with your case open. You will see several cable(s) running from the motherboard to the drive(s). SCSI cables are generally thicker shielded thant IDE with either 50 or 68 pins(I think the newest interface is 80 pins). IDE cables are only 40 pins.

If your hard drive is connected to a card in a PCI slot, then it’s an added card and you already have built-in IDE interfaces(of course without motherboard and computer specs I don’t know if it will support ATA/66).

-Sam

10

pricewatch.com

I used that to find my scsi drive.

11

You’re missing the point GaWd. It’s not a matter of how fast the two different types of drives read and write data it’s what happens behind the scenes.

A SCSI drive gives a CPU hit of about 2% whereas an EIDE drive can nail your CPU for 33% or more. Games (which is where I said you can notice a difference) are consistently pegging your CPU usage up near the top (75%+). When an IDE drive engages it demands processor time which is no longer available to the game causing the game to stutter.

This, of course, is not an issue when using a standard office app. Once an office app is loaded the CPU generally has nothing to do so who cares if on occasion your drive sucks up 33% of processor overhead…you’ll never notice it.

12

Unless you system is quite old or a very high end server type (unlikely) you have a very good chance of already having an EIDE controller onboard.

You can check this without opening your system. You need to go into your BIOS setup and see if there are setup parameters for an IDE controller (BIOS may call it “onboard” or “ATA” controller). If the controller is defeated in setup you need to make it active and the system will recognize it. The IDE controller typically uses IRQs 14 and 15, so if you’ve got anything sitting there now you will potentially have a conflict unlkess you re-allocate what is currently using these IRQs (*if anything) unless the controller is already active and using them.

It still might be a good idea to get a ATA 66 PCI add in EIDE card as the latest drive sizes (20 gig+) can give some older (and not so old) BIOSes a real bellyache.

If you decide to go this route email me and I’ll give ou step by step instructions for preparing your new drive and transferring your old drive contents to your new drive. There are a few tricks involved but you don’t need a special program like Ghost. Win98 xcopy32 commands in protected mode will do everything you need.

13

You CPU resource consumption quote for EIDE of 33% is not entirely accurate. With the Win98 DMA option enabled (available on virtually any EIDE drive/MB controller combo sold in the last 5 years) resource consumption for processing ATA drive commands with DMA enabled will typically be below 10% and often lower. They may occasionally be higher bursts but on any properly configured, minimally competent system with a 300 mhz or better CPU, overall EIDE resource consumption should be minimal.
See http://www.storagereview.com for a more complete discussion of the resource consumption issue.

Part of SR site EIDE / SCSI discussion quoted below.

Since the market has come to be dominated by the two interface standards, IDE/ATA and SCSI, the question of “which is better” has been bandied about endlessly on the Internet and in other places as well. The simple answer is that neither is better than the other, absolutely. Why? Because if one were clearly superior to the other in every way, the superior one would have taken over the market completely and forced the other one out. The fact that both are in common use (and have been for many years) proves that both have valid reasons for being on the market. Contrast this to the older ST-506/412 interface, for example, which was obsoleted by IDE/ATA since it had no advantages to cause it to persist, and disappeared very quickly.

Whether IDE/ATA or SCSI is better depends on what your needs are, and how much you are willing to spend. In this section I attempt to put the issue in perspective by looking at various performance and quality aspects of the interface and seeing how IDE/ATA and SCSI stack up at each. Of course this will be colored somewhat by my own experience and biases (the entire web site is–that’s just life). However, I am attempting here to be as objective as possible in contrasting the two interfaces, and trying to be comprehensive in looking at all of the aspects that are relevant to making a decision.

A primary deciding factor in the SCSI vs. IDE/ATA question is the number of devices you plan to use (or use in the future) in your system. In many respects, IDE/ATA is superior if you are using only one, two or three devices such as hard disks or CD-ROMs. If you are using many devices, say over four, then SCSI is superior to IDE/ATA in several different respects.

Cut To The Chase

I still think it is best to read all of the other sections in this area and look at how IDE/ATA and SCSI compare in various respects. However, I realize that (as usual) I have made this large by blabbing too much and perhaps some people are looking for a quick answer. Just recognize that a short answer is rarely as good as a long one.

Overall, the SCSI interface is technologically superior to the IDE/ATA interface. It supports more devices, allows for better multitasking, more expansion, use of more high-end devices, more types of devices, and more performance-enhancing features. IDE/ATA is intended primarily for PCs that are not using a lot of peripherals, or for those that are cost conscious.

For the average person who is using their PC for light office work, games, internet use, etc., I still recommend IDE/ATA. The reasons are simple: cost and simplicity. Virtually all PCs today ship with IDE/ATA hard disks standard, and if you are using a small number of devices–say one hard disk and one CD-ROM drive, IDE/ATA is more than adequate performance-wise for the typical office or home user. As long as the machine is reasonably modern and the PC is set up properly, IDE/ATA will work without much difficulty, and there is no need to special-order or customize the machine, since it is really the “standard”. The cost of a simple IDE/ATA setup is far less than an equivalent SCSI bus.

For the user who is performance-conscious, who will be doing real multitasking, using many devices at once, doing heavy development work, supporting multiple users at once on the machine, or who otherwise wants the best and is not afraid if it costs a few hundred dollars more, SCSI is the obvious choice. SCSI offers the most flexibility, the most choice of peripherals, and the best performance in a multitasking or multi-user environment.

So if you are looking to set up a low-end or middling system, I would say SCSI is out of the question. The simple reason is that for the additional cost of going to SCSI, you could probably improve overall performance more by buying a faster processor, more system RAM, or a faster hard disk. For a high-end system, SCSI has definite advantages and is preferred.

Also bear in mind that there are some peripherals that generally are only available on SCSI, or that have significant enough advantages on SCSI that if you want to use this type of device, SCSI is pretty much a must. Scanners and CD-R drives come immediately to mind. Once you make the decision to go with SCSI, the cost of going to SCSI for your hard disks is reduced because you’ve already made the commitment for the host adapter, which is the large up-front cost of SCSI.

The final, real bottom line is: if you want it cheap and simple, use IDE/ATA. If you want performance and flexibility and have the money to pay for it, use SCSI.

Cost

The IDE/ATA interface is superior to the SCSI interface in terms of cost in virtually every way. (The only exception would be if you needed to use, say, 10 devices, in which case SCSI might be cheaper because this would require a special solution to do in IDE/ATA. I am assuming that nobody would use IDE/ATA for this many drives anyway.)

Here are four reasons why SCSI is more expensive than IDE/ATA:

Additional Hardware: SCSI setups require a host adapter, which means either an add-in card or a more expensive motherboard. For using external devices there is also the matter of cables and other one-time costs.
Lower Volume: Far fewer SCSI devices are sold than IDE/ATA devices. The price of an item manufactured in high volume is usually less than one manufactured in low volume.
Niche Market: Since SCSI has a reputation for being higher-performance and is generally used by those who are less cost sensitive, sellers can afford to run higher margins and still make the sale, and will usually do so.
More Advanced Technology: This is really a matter of appearances: since the performance-conscious use SCSI, it is the interface where the most advanced new drives will typically show up first. New technology is more expensive than old technology. Too often, people compare a “4 GB IDE drive” to a “4 GB SCSI drive”, where the 4 GB is old and slow, and the SCSI drive is new and fast. This is an apples-and-oranges comparison that has nothing to do with the interface.
For those for whom cost is an important consideration, IDE/ATA will win over SCSI virtually every time. For low-end systems, the extra funds required to go to SCSI will usually be better spent upgrading core parts of the system such as the processor or system RAM.

Performance

Comparing the performance of the SCSI and IDE/ATA interfaces is not an easy task. While those who favor SCSI are quick to say that it is “higher performance” than IDE/ATA, this is not true all of the time. There are many different considerations and performance factors that interact when considering the performance equation, because performance is so dependent on system setup and on what is being done with the PC. I will try to look at some of these factors and how they influence system performance for both interfaces:

Device Performance: When looking at particular devices, there is theoretically no difference between SCSI and IDE/ATA. The device itself should be the same in terms of its internal performance factors. In practice, this isn’t always the case. Many manufacturers only make a particular drive as SCSI or IDE/ATA, not both, so direct comparisons aren’t easy. Since SCSI is known to be the choice for those seeking performance, higher-performance drives tend to show up on the SCSI interface well before they do on IDE/ATA (you pay for this performance, of course, but that’s a separate issue). Another issue is the implementation of the integrated device controller logic and the interface chip. Some companies that produce the same device (the physical hard disk assembly, for instance) for both SCSI and IDE/ATA may do a much better job of writing the control logic for one interface than for another.
Maximum Interface Data Transfer Rate: The interface or external data transfer rate describes the amount of data that can be sent over the interface. The highest-bandwidth SCSI bus is currently Ultra Wide SCSI, which has a maximum throughput of 40 MB/s. The highest-bandwidth IDE/ATA standard is Ultra ATA, which has a maximum of 33 MB/s. These are close enough that a difference will only be seen in the very most demanding applications. In fact, considering that you can only have two devices on the bus with Ultra ATA, the 33 MB/s rate will never be fully exploited using today’s technology. The 40 MB/s of Ultra Wide SCSI will only be saturated if you are using several devices. Since this is possible with SCSI, it gets a slight nod here, but this isn’t much of an issue.
Single vs. Multiple Devices and Single vs. Multitasking: For single devices, or single accesses (as in DOS), in many cases IDE/ATA is faster than SCSI, because the more intelligent SCSI interface has more overhead for sending commands. If you are just using a single hard disk, or doing simple work in DOS or Windows 3.x where everything happens sequentially, most of the benefits of SCSI are lost. For multitasking operating systems, especially where transfers are occurring between multiple devices, SCSI allows multitasking and command queuing, which enables devices to set up multiple transactions and have them take place basically simultaneously. In contrast, IDE/ATA transactions to one device “block” the channel and the other device cannot be accessed. Putting two devices on two different channels allows simultaneous access, but severely restricts expandability. IDE/ATA still does not have the advanced features that SCSI has for handling multiple devices.
Bus Mastering: While newer PCs allow the use of PCI bus mastering for IDE/ATA devices, in practice, the SCSI implementation is superior, offering better performance with far fewer problems and less resource use by the system processor.
Device-Mixing Issues: IDE/ATA channels that mix hard disks and CD-ROMs are subject to significant performance hits in some situations, due to the fact that these are really different protocols on the same channel. SCSI does not have this problem.
Overall, SCSI is a higher-performance interface. For very simplistic applications, like a single hard disk and a single CD-ROM drive, IDE/ATA has a marginal advantage. For complex applications, SCSI has a significant advantage.

Configuration and Ease of Use

Much like the performance issue, the winner here depends on how many devices you want to use. Both IDE/ATA and SCSI have had a rather spotty history in terms of their ease of setup and configuration, and both are much better today than they have been in the past. Overall, I would say that IDE/ATA is easier to set up, especially if you are using a reasonably new machine and only a few devices. Its support is built into the BIOS, and there are fewer issues to deal with: no different cable types, no bus to terminate, fewer issues with software drivers, and fewer ways in general that you can get yourself into trouble.

This advantage for IDE/ATA drops off quickly if you want to get maximum performance while using more than two or three devices. You then have to worry about where they are being placed on the channel, finding IRQs and other resources for multiple channels, etc. This can be done without too much difficulty, but there are many different things to take into consideration. In contrast, once SCSI is set up, you can put 7 devices on the bus (or 15 for wide SCSI) with very little effort, although you do have to watch the termination as you expand the bus.

SCSI has a significant advantage over IDE/ATA in terms of hard disk addressing issues. While IDE/ATA hard disks are subject to a host of capacity barriers due to conflicts between the IDE/ATA geometry specifications and the BIOS Int 13h routines, SCSI is not.

Expandability and Number of Devices

SCSI beats IDE/ATA hands down here. A regular SCSI bus can support 7 devices and a wide SCSI bus 15. IDE/ATA can supposedly support 8 devices if you use all four IDE/ATA channels that are theoretically defined, but this is extremely rarely done because there are system resource and software support issues.

Device Type Support

SCSI beats IDE/ATA clearly in this regard. IDE/ATA supports hard disks and ATAPI devices such as CD-ROM drives and some tape drives. SCSI supports these and many more devices including scanners and CD recordable drives.

Device Availability and Selection

While there are many more types of devices available for the SCSI platform, there are generally more choices of any given type of device for IDE/ATA. While IDE/ATA supports basically hard disks and CD-ROM drives, there are many more different brands and types of hard disks and CD-ROMs around for IDE than for SCSI.

Software / Operating System Compatibility

While much less of a problem today, SCSI has traditionally been not as well supported as IDE/ATA, due simply to the fact that it was less common. DOS and Windows 3.x do not provide native SCSI support (but do support SCSI through the use of drivers). Windows 95 and Windows NT do support SCSI directly, as do the various UNIX implementations.

System Resource Usage

Generally speaking, SCSI is superior to IDE/ATA in this regard. If you are only using a single IDE/ATA channel, the two are basically a wash in terms of resource usage. However, once you go to a dual IDE channel situation you will generally use more resources than SCSI uses. If you were ever to set up a four-channel IDE implementation you would be using significantly more resources than if you had just set up a SCSI bus.

14

So, I can use SCSI for some of my devices, and IDE for others? And the ones on SCSI won’t count towards the maximum that IDE can handle?

15

That is correct.