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Re: [TCLUG:12134] SCSI vs. IDE



With SCSI all the CPU has to do is dump data to the SCSI controller. 
With IDE the CPU can't off-load the work, it has to control where the
read/write head goes, if the drive is spun up...i.e. handle all the gory
details.

"Eric M. Hopper" wrote:
> 
> On Tue, Jan 11, 2000 at 04:30:09PM -0600, Chris McKinley wrote:
> >
> > The disk transfer rate is limited not by the interface, but by the
> > spindle speed.  The bus transfer rate then dictates the number of
> > drives you can have before you get I/O contention.  IDE, even ATA66,
> > can only fill the bus for the size of the drive buffers, whereas a
> > properly striped RAID setup can keep sustained data flows.  Other
> > advantages are that SCSI supports up to 15 devices / channel, SCSI
> > supports other devices than storage, and SCSI uses less than half the
> > CPU resources of IDE.
> 
>         Hard data, yes!  :-)
> 
>         OK, suppose you hook up 4 hard-drives to your IDE interface and
> use software raid to stripe aross them?
> 
>         Your comment about CPU indicates that SCSI is better for even
> one drive.  This mirrors an experience I had when I was running a heavy
> test that read and wrote random 8 meg segments of a 64 meg file.  My
> machine slowed down to a crawl and all the CPU time was being spent on
> 'system'.
> 
>         Why does IDE use more CPU?
> 
> Thanks,
> --
> Its name is Public Opinion.  It is held in reverence. It settles everything.
> Some think it is the voice of God.  Loyalty to petrified opinion never yet
> broke a chain or freed a human soul.     ---Mark Twain
> -- Eric Hopper (hopper@omnifarious.mn.org  http://omnifarious.mn.org/~hopper) --
> 
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-- 
Adam Maloney
Systems Administrator
Internet Exposure, Inc.