Benefits of SCSI

Aside from raw speed, what, theoretically, is the advantage of SCSI over IDE?

The problem I have is that I have read some stuff on the issue on the web which states test results rather concisely but do a terrible job of explaining how the two technologies work (other than a fixed hardware address vs. a dynamically assigned one, but what are the repercussion of that?). I have tried asking about this at other places and have been disappointed with responses from people who obviously don't really know any better than I. I am hopeful, given that this is the "DEEP" end of the pool, that I might find out here. If this doesn't work I'll order a book on the subject.

I have a hypothesis of how it works. Since SCSI devices have fixed addresses, including the controller itself, if you transfer information from one device to another connected to the same SCSI controller the data can go straight between the two devices and not involve the motherboard in the transfer. But, for some reason I don't know, IDE can't do that.

I have read that for operation involving only one device, IDE is nearly identical to SCSI in terms of speed and CPU overhead.

Data is supposed to be able to go between devices directly. You can have more devices on a scsi bus, you don't have to worry about slaving and mastering, drives communicating on the same channel don't interfere with each other like ide, the drives are typically higher quality, and of course, scsi is faster.

Do you know where I can find a removable SCSI hard drive bay?

Might poke around on www.hypermicro.com

They seem to have a pretty good selection of random scsi stuff. I see external enclosures there, you'll have to dig for internal ones, I didn't notice any.

Ok there are a few advantages to SCSI.

1) The drives are faster. You have 15kRPM drives which give a much lower seek time and hence better random access speeds. Also with increased rotational speed the read speed is faster because the data passes under the head faster.

2) The interface is much more effiecient especially over multiple loads or different drives.

3) Due to more effiicent and powerful controllers the CPU utilization is reduced by a large amount

4) reliability. They are simply more reliable.

5) TCQ (Tagged command queuing) the SCSI interface will change the order that it has to do things inorder to make things faster.

6) In responce to your last line. This is true. IDE is faster wiht only 1 drive. THis is due to lower protocol and command overheads. Though once you have more than 1 drives this is eliminated

If thsi doesnt contain enough info and you want more reading go to http://www.storagereview.com

SCSI no go

Well, forget SCSI because I just learned that the Yamaha CRW-F1 was discontinued. Since the benefit of SCSI is partially based on having more than once device on the same controller I had decided long ago that it wouldn't be worth it without a top-of-the-line SCSI CD burner. I already know the #2 brand for CD-burners: Plextor.

Actually, I'll probably get an external Firewire CD burner when I get one.

While I'm at it, does anyone know where I can get a removable hard drive bay for IDE? I want to have one drive for Linux and one for Windows.

Another benefit of SCSI is that it can be used to build cluster machines and IDE cannot.

mugambo said:

Another benefit of SCSI is that it can be used to build cluster machines and IDE cannot.

Click to expand...

What exactly do you mean?

Several computers sharing a cluster of (hdd) devices?

Yes, but it is with the Windows 2000 Enterprise (or datacenter) "Cluster Service" running. I use it for automatic failover for my SQL Server 2000 implementations; you cannot activate the "Cluster Service" unless you have either (1) SCSI or (2) fibre optic drives. (Yes, you can also build "1-box" clusters.) My understanding is that with Linux you can build clusters using firewire also.
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Dave