Re: [NAL] Re: OT: SCSI better than IDE?
On Monday 29 December 2003 09:39 am, Bijan Soleymani wrote:
> On Mon, Dec 29, 2003 at 10:36:49AM +0000, Rus Foster wrote:
> > > Interesting, Paul. So are you saying that SCSI hard drives are
simply
> > > not worth the extra money or that the advantages of SCSI are in
the
> > > interface and not in the media?
> >
> >
> > IMHO SCSI disks last longer so its worth paying extra there. Also
the
> > interface for SCSI is just better as the controller handels the disk
> > rather than IDE which is done more on the CPU
> This is no longer true. Most current IDE controllers support various
> DMA schemes. Like ATA-100, ATA-133, etc. So with IDE the controller
> now bypasses the CPU too.
This IS still true - there's more of a difference than DMA. SCSI drives
allow multiple outstanding requests _per drive_, let alone per bus.
This means that the drive can choose to complete the requests in
optimum seek order, which cannot be determined by the host, which does
not have access to internal drive geometry. Also, while the drive is
transferring a block, it is already seeking to the next request. With
IDE, the data transfer must complete before the next request even
reaches the drive. The ATA standard describes queuing/disconnect
behavior; it just isn't widely implemented.
> Now it may be true that SCSI drives have better performance, but right
> now I think that's just because they're better drives (mechanically,
> and electronically) rather than because of the controllers. They're
> also *much* more expensive.
Even when the same mech is available with either SCSI or IDE, the SCSI
price is higher. It's a simple matter of volume - SCSI volumes are
low, so costs and prices are high. When a low volume drive (very high
performance and cost) is made, there really isn't any savings to go
IDE, and the target market for such drives usually desires SCSI anyway.
--
Rob
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