Subject: Re: AHA-2940 UW SCSI adapter problems?
To: <>
From: Michael Parson <>
List: port-i386
Date: 07/19/2005 11:00:23
On Tue, Jul 19, 2005 at 11:41:38PM +0800, wrote:
> Quoting Hauke Fath <>:
>> Am 19.07.2005 um 8:25 Uhr -0700 schrieb Andy Ruhl:
>>> I don't think the 2940UW is going to work with that disk, isn't that
>>> an LVD disk?
>> LVD disks will happily fall back to SE SCSI if needed.
>> 	hauke
> Oh joy, it will work then?  I've just googled quickly for that,
> and don't understand a word of it (LVD vs. SE) but I'll spend
> some more time on it today.
> I should get myself a book on SCSI as well.
> Are SCSI disks really all they are cracked up to be?  Is SCSI vs.
> ATA just a religious war, or are there technical merits to SCSI?

Modern SCSI (U320) verses Modern IDE (S-ATA?/or P-ATA133) the features
are closer than they once were back in the Fast SCSI vs PIO mode IDE
days, but there are still differences.

Keep in mind, I'm talking in generalities here.

SCSI disks tend to be made a little better, tested more, etc, and aimed
at high-end workstations and servers.  IDE disks tend to be thought of
by their manufacturers as consumer grade products.

SCSI is a bus, each device on the bus is intelligent and is capable of
doing it's tasks, for the most part, w/o the CPU.  The computer tells
the SCSI device what to do, that device can do what it was told and the
CPU can move on, just listening for the SCSI device to return with an
"I'm done" message.  Newer IDE (ATA) is acting more and more like this.
Once upon a time, disk I/O with IDE disks was CPU intensive.

Another big thing SCSI gave you was the number of devices you could plug
in.  In SE SCSI, you could have up to 7 devices, these days, you can go
to at least 14.  When you get into things like FC, that number keeps
going up.

P-ATA still has a 2 device/chain limitation.

SCSI does more than just storage.  I've had, and still have, SCSI disks
and tapes, but there are also SCSI scanners, ethernet, even PCMCIA.

IDE is, for the most part, just storage.

Back when my home boxes were Amigas and Macs, I was a SCSI bigot, and
rightfully so.  These days, I just can't justify the cost/benefit.
Especially when Seagate is doing a 5 year warrantee on their IDE stuff.

With your 2940UW, you're not going to see as many benefits over today's
ATA stuff.  IIRC, UW was 40m/s, so even an older ATA100 disk would boast
higher burst throughput on a single device.  Loaded with 7 disks though,
the SCSI would show what it was made of. =)

Michael Parson