[rescue] Sun Blade 100 Question - IDE

[Gregory Leblanc]

On Fri, 2002-05-10 at 22:04, Patrick Giagnocavo wrote:
> On Sat, May 11, 2002 at 12:32:29AM -0400, George Adkins wrote:
> > On Friday 10 May 2002 11:32 pm, Patrick Giagnocavo wrote:
> > > > Thpplt!  Even 1 SCSI bus can handle 6 drives.  So to keep from getting a
> > > > performance hit, you have to limit yourself to 2 drives.  I know I sound
> > > > like a jerk, but I really think that's crap.
> > >
> > > Remember that IDE got its start from about 1989 and was designed to be
> > > low cost.  Desktop drives of that era were stuffing maybe 200KB/second
> > > through the channel.
> > >
> > This is no excuse for the apalling lack of foresight and piss-poor 
> > engineering.  it's right in there with "Who'll ever need more than 640K..."
> 
> You gotta be careful when you say those kind of things while defending
> SCSI.

OK, you asked for it.  :)

> What about the way you can blow up stuff by mis-matching HVD and SE
> SCSI?  Why did they keep the same connector - they could have
> easily keyed it somehow, or put in a small CPLD to figure out if
> something wasn't right and avoid damage.

No argument there, but the second attempt got it right.  LVD and SE are
"compatible".

> What about the original 8-bit SCSI spec?  What about drive size

What about it?

> limitations?  Go ahead, plug in an earlier SCSI device to your U160

I hear that they exist, never ran into them, though.

> device chain and watch performance go down...

Well, there is that, but I don't know how to make that not happen and
still have things work reliably.  

> In theory, SCSI is backwards compatible, but the price to convert
> between the various interfaces via cabling or tailgates often does not
> make sense from a cost standpoint.

In theory?  I can use a U160 drive on a SCSI-2 controller, and it will
saturate the bus on it's own 5 times over.  No problems there.  I've run
original SCSI 2 drives connected to my newest SCSI controllers (at the
moment, and Adaptec 3940UW) and they work fine.

> IDE at least will never blow up stuff, is completely backwards
> compatible (aside from a few drive issues when putting an old Conner
> and old Seagate on the same channel), and the connector hasn't changed.

Uh, yeah, right.  It's no more backwards compatible than SCSI is.  Ever
hook an 80GB drive up to the VESA hard drive controller in a 486?  It
sure doesn't LOOK like an 80GB drive.  

> Connectors for SCSI include:
> 
> 50-pin centronics
> 25-pin "Apple SCSI"

This is the only bad one, as far as I'm concerned.

> 50-pin micro-D
> 68-pin 
> 80-pin SCA

You left out at least VHDC, 50-pin ribbon cable, 68-pin ribbon cable,
and probably several others that I'm too tired to think of (yeah, ok, 2
of those aren't connectors, but I'm not enough of an electronics wienie
to know what to call them, yet).

> I am not flaming you, just pointing out some stuff that shows that
> SCSI isn't perfect either.  And many early SCSI devices are not
> exactly compliant.
> 
> Let's just say that current SCSI has advantages for multiple drives,
> for hot-swap (in terms of implementations, it is easier to find
> hotswap SCSI than hotswap IDE) and for some other stuff.

The IDE spec doesn't make any provisions for hot-swap that I can find. 
There are some things that hack hot-swap into IDE, but only if you're
lucky does it work.  Hot-swap SCSI is trivial, except under Linux.  :-)

> Let's say that IDE has advantages in terms of price/performance and
> generally higher storage capacity (higher capacities come out first in
> IDE format due to SCSI user's emphasis/preference for IOPs).

Erm, no, let's not.  Let's say that IDE has advantages in terms of
price/storage capacity.  SCSI has an EASY win on performance for a given
price, once you're talking about reasonable amounts of performance.  IDE
can't handle multiple reads to a given controller worth a darn, and SCSI
manages that without a sweat.  And if you want to put together a lot of
bandwidth (200MB/sec+), IDE is going to be very very very very hard
pressed to deliver at any price, let alone at a price that's in
competition with SCSI.

Hopefully it's not too late at night for me to have written this.  Write
it off to the beers that I didn't have at the ballgame tonight.  :)
	Greg

-- 
Portland, Oregon, USA.
Please don't copy me on replies to the list.