IDE & SCSI (IDE vs. SCSI)?

IDE & SCSI (IDE vs. SCSI)?

Post by David J. Toppe » Wed, 10 Dec 1997 04:00:00



Howdy Y'all,

I'm driving myself nuts about purchasing some new machines for the lab.
The reason it's difficult is because most vendors (eg., Gateway,
Quantex, Compaq, etc...) are using that Adaptec AHA2940 SCSI controller
... and for some reason I've forgotten, I really want to use SCSI.

Some questions:

Is it possible to use BOTH SCSI and IDE drives in the same box?

What are the real advantages of using SCSI over some of the new ATA mode
4 IDE drives?

The machines will be in a networked environment, but I can set things up
so that folks do a lot of work locally (eg., on a local IDE drive) and
store user directories and such on some other machine with a SCSI drive.

I'd love to hear from folks on these issues.

BTW:  the lab does alot of digital audio work currently ... moving up
towards more graphics and other multimedia later.

Thanks,

Dave Topper
--
Technical Director
*ia Center for Computer Music

 
 
 

IDE & SCSI (IDE vs. SCSI)?

Post by Christopher Brow » Wed, 10 Dec 1997 04:00:00


On Tue, 09 Dec 1997 17:34:07 -0500, David J. Topper


>I'm driving myself nuts about purchasing some new machines for the lab.
>The reason it's difficult is because most vendors (eg., Gateway,
>Quantex, Compaq, etc...) are using that Adaptec AHA2940 SCSI controller
>... and for some reason I've forgotten, I really want to use SCSI.

>Some questions:

>Is it possible to use BOTH SCSI and IDE drives in the same box?

Yes.  My "Cyrix-based" host, knuth
(<http://www.hex.net/~cbbrowne/hardware.html#KNUTH>), uses both at the
same time.

Quote:>What are the real advantages of using SCSI over some of the new ATA mode
>4 IDE drives?

The fastest EIDE's are probably faster than "traditional" SCSI-2 from an
I/O management perspective, but not the UltraSCSI, and certainly not the
Ultra/Wide-SCSI.

It still *appears* that IDE doesn't buffer commands the way SCSI does;
this doesn't gain you much until you have more than one drive.  With 2
or more drives, performance of a SCSI system should be significantly
faster.

It's also not clear whether the latest IDE adaptors buffer data the way
SCSI does; with SCSI, the CPU should be blocked only for the instant
that data is being updated from SCSI host adaptor' buffers.  

With IDE, it *used* to be that the CPU would be blocked for the time it
took to pull data off the drive.  There are some claims to the effect
that performance has substantially improved in this regard for EIDE;
that may require that you use special EIDE controller hardware that may
not yet be supported under Linux...

--

"Bother," said Pooh, "Eeyore, ready two photon torpedoes and lock
phasers on the Heffalump, Piglet, meet me in transporter room three"

 
 
 

IDE & SCSI (IDE vs. SCSI)?

Post by Ryan Rinald » Wed, 10 Dec 1997 04:00:00


Just pointing out that most BIOS will place the SCSI drive(s) under all ide
devices..excluding CD-ROM's

 
 
 

IDE & SCSI (IDE vs. SCSI)?

Post by Mike Campi » Thu, 11 Dec 1997 04:00:00



Quote:>Is it possible to use BOTH SCSI and IDE drives in the same box?

Yes, but you will probably have to boot from SCSI. I have heard that you can
leave the IDE stuff out of you BIOS, boot from SCSI, and then install an IDE
driver.

Quote:>What are the real advantages of using SCSI over some of the new ATA mode
>4 IDE drives?

SCSI allows more devices to be connected. Up to 15 with the newer cards. In
addition, you can connect scanners and external disks which you can't do with
IDE. You also don't have to put all those IDE parameters into BIOS. The latest
SCSI goes up to 80 MB/s compared to 33 MB/s for IDE. The new 10,000 RPM drives
have a sustained transfer rate in the range of 20 MB/s. With the right hardware
and software you also get RAID capability.

Quote:>The machines will be in a networked environment, but I can set things up
>so that folks do a lot of work locally (eg., on a local IDE drive) and
>store user directories and such on some other machine with a SCSI drive.

It is very common in a corporate environment to install the operating system on
the local drive and the user files on a remote server. It greatly simplifies
the backup strategy and security. Many servers also have a UPS.

-Mike Campin

--
              ____________________________
             /                            \
            /         Mike Campin          \

          / http://www.hash.com/users/campin \
         /____________________________________\

Life is much simplier if you don't know what is going on.

 
 
 

IDE & SCSI (IDE vs. SCSI)?

Post by Mark Ha » Thu, 11 Dec 1997 04:00:00


: The fastest EIDE's are probably faster than "traditional" SCSI-2 from an
: I/O management perspective, but not the UltraSCSI, and certainly not the
: Ultra/Wide-SCSI.

you're mistaking the bandwidth of the bus for the speed of the drive.
good 7200 rpm scsi disks sustain around 10-15 MB/s, regardless of whether
they're on a fast/wide, ultra, ultra/wide, Ultra2, FC-AL, FireWire, etc.
as long as the bus bandwidth is greater than the sustained bandwidth
of the drive, you're golden.  naturally, multiple drives complicate this.

: It still *appears* that IDE doesn't buffer commands the way SCSI does;

ATA drives do indeed not do tagged command queueing, and as far as I know,
you can't have active command (even seeking) on both drives on a chain
at once.  ATA drives can and do read-ahead and write-behind, though,
if that's what you meant by buffering.  and nice/big/fast/modern ATA drives
come with 512K cache, nothing to sneeze at.

and of course, they're dirt cheap!  under $50/GB.

: It's also not clear whether the latest IDE adaptors buffer data the way
: SCSI does; with SCSI, the CPU should be blocked only for the instant
: that data is being updated from SCSI host adaptor' buffers.  

it's quite clear: motherboards have had busmastering ATA on board for
quite some time now, which most definitely does not "block" the CPU.

: that may require that you use special EIDE controller hardware that may
: not yet be supported under Linux...

no.  the 430fx chipset, circa 2 years ago, did BM-IDE,
and Linux supported it promptly.

regards, mark hahn.
--

                                        http://neurocog.lrdc.pitt.edu/~hahn/

 
 
 

1. 2.5.1-pre2 compile error in ide-scsi.o ide-scsi.c

You patch is reverted and I don't think it will cut it,
since I tries this myself and it didn't work out.

BTW>. Anybody out there who managed to make
SCSI gogin on 2.5.1-pre2... I only have PPA ZIP and
IDE-SCSI at my home machine, and both fail with a bad
pointer derefference...
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