[1936] in linux-scsi channel archive
Why SCSI disks rather than IDE disks? Re: SCSI disks
daemon@ATHENA.MIT.EDU (Edward Welbon)
Mon Jun 2 12:04:17 1997
Date: Mon, 2 Jun 1997 11:00:29 -0500 (CDT)
From: Edward Welbon <welbon@bga.com>
To: "W. Reilly Cooley" <wcooley@navi.net>
cc: linux-scsi@vger.rutgers.edu
In-Reply-To: <Pine.LNX.3.91.970602002158.2287B-100000@rheingold>
I redirected this to linux-scsi as the topic seemed more appropriate to
that list.
On Mon, 2 Jun 1997, W. Reilly Cooley wrote:
> I hate to continue to beat this subject into the ground, but exactly
> what are SCSI hard drives considered to the superior to IDE?
The disk mechanism itself is not at issue as those are in principle
identical. The style of drive electronics (interface) is where the
principal difference is. A few reasons for scsi disks and scsi in
general:
(1) Reduced CPU demand for increased system performance.
(2) Multiple device support.
(3) Support for external devices (i.e., not just internal devices).
(4) Expanded peripheral support (scanners, tapes, etc).
(5) Hardware/Software compatibility.
(6) Multi-tasking capabilities.
(7) Easy upgrades.
For further information I recomend "Understanding I/O Subsystems" by W.
David Schwaderer and Andrew W. Wilson Jr. It doesn't have a great deal of
nuts and bolts stuff (i.e., no "how to take the covers off of your system"
type of stuff) but it has an excellent description of the "theory"
behind PC-like IO. It also discusses the sordid history of the evolution
of the original IBM PC to those of today (that was worth the price of the
book - it explains many of seemingly senseless design decisions one sees
in PC's). In particular, there are detailed (yet clear) chapters on the
flavors of IDE and a corresponding chapter for SCSI (it even includes SSA,
IEEE1394 and FC-AL). I plagarized the above seven points from that book.
> It seems to be generally considered that SCSI is superior to IDE, but from
> this guy's writing (excepting for multiple devices on the SCSI bus or really
> fast HDs) SCSI provides no benefit. Pls. someone cursorily clarify.
If you are not concerned with fast disks and do not plan on having many
peripherals, then IDE is fine. If you wanted say, two disks, a tape, a
cdrom, a printer and a scanner then you may have a lack of external IO
ports in the usual PC and will need to add some kind of external interface
card anyway. If you start off with SCSI you will be much better prepared
to meet this possibility. There are many valid reasons to choose IDE.
There are many valid reasons to choose SCSI. Only you can evaluate the
trade-offs based on your personal goals etc.
Ed Welbon; welbon@bga.com;
<a href="http://www.bga.com/~welbon/arachnid.html">the arachnid mail list</a>
