Linux-kernel mailing list archive 2000-23,: Re: ULTRA ATA/100 announced

# Re: ULTRA ATA/100 announced

J. S. Connell (ankh@canuck.gen.nz)
Tue, 6 Jun 2000 07:42:19 -0700 (PDT)

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On Tue, 6 Jun 2000, James Sutherland wrote:

> How much would a four channel SCSI card cost me? A lot more than four IDE
> channels, I suspect? Now how much do IDE and SCSI drives cost - the same?
> Not quite...

That overlooks the fact that four SCSI channels gives you 60 disks, and
four IDE channels gives you _eight_ disks. And yes, a four-channel SCSI
card will cost a fortune, but only because there's limited demand for
them[0]. Want eight disks? Try comparing the price of _one_ SCSI
controller vs. two Promise cards. Not quite as much of a difference now.

(While we seem to be whinging and whining about IDE vs. SCSI, let me throw
this in: with _one_ SCSI controller, which uses _one_ interrupt and _one_
piece of I/O space, I can support 30, sometimes even 60 disks. To get even
30 disks in a box with IDE, I'd need anywhere between three and eight IRQs
and I/O port ranges[1], and seven free PCI slots[2]!)

SCSI disk prices vs. IDE disk prices can be seen as a function of supply
and demand. Yes, the actual disks (excluding circuit board) are identical,
yes, the circuit board probably costs $5. A disk without a controller,
however, is called a "paperweight". As the demand for IDE disks exceeds
the demand for SCSI disks, fewer of the latter are produced. (I'm almost
willing to bet that if IDE never existed, SCSI disk prices would be about
where IDE is now.)

IDE and SCSI, in my mind, are addressing two different segments of the
market. Let's just shut up about it and use whichever is most suitable for
whatever we're trying to do, okay?

--Jeff, eagerly awaiting the flames. (Let me just empty the bit-bucket first.)

[0]Same thing happens with single-ethernet boards vs. quad-ethernet boards.
The quads cost quite a bit more than 4x the cost of a single.

[1]Yes, IRQ sharing exists, and yes, the Promise drivers will do that.
But I still need a minimum of three IRQs, since nothing tries to make my
onboard IDE channels share either with each other or with the Promise
cards.

[2]Unless someone's come up with an IDE controller that -- horrors! --
supports more than two channels on one card.

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