[rescue] Macs & IDE vs. SCSI

Phil Stracchino alaric at caerllewys.net
Sat Apr 12 12:43:42 CDT 2003

On Sat, Apr 12, 2003 at 12:55:00PM -0400, Patrick Giagnocavo +1.717.201.3366 wrote:
> On Sat, Apr 12, 2003 at 12:32:48PM -0400, Phil Stracchino wrote:
> > On Sat, Apr 12, 2003 at 06:58:37AM -0700, Lionel Peterson wrote:
> > Frankly, beyond a certain point, as far as the actual speed of the
> > drive is concerned it's all moot anyway.  Once you fill (or empty) the
> > drive's buffer, you're back to the native sustained transfer rate of the
> > disk mechanism, which is nowhere close to keeping pace with any current
> > disk interface.
> Don't forget protocol overhead as well.


> > Where SCSI's speed advantage comes in is that it supports disconnection,
> > so it can go off and do something else on another drive while that one
> > reads more data instead of having to wait for one drive at a time to
> > finish as on IDE, and that doing so consumes negligible resources on the
> > host.  On a resource consumption basis, one should think of "IDE disk"
> > in the same breath as "host-based printer", "winmodem", and unaccelerated
> > dumb framebuffers.
> I agreee on the disconnection speedup but as for "winmodem":
> Argh... this is simply not true.  When you are using "UDMA Mode 2" or
> anything faster or more recent than that, the transfers from disk to
> CPU are done exactly the same way as a SCSI adapter does it (DMA
> transfer direct to memory, then 1 interrupt to tell the CPU that data
> is there).

Well, OK, maybe "winmodem" was exaggerating a bit.  Mea culpa.

I stand behind the rest of my points though.

(They make good cover in case of incoming fire.)

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