Date: Wed, 12 Jun 1996 02:53:08 -0700 (PDT) From: Brian Litzinger <brian@MediaCity.com> To: john@ulantris.infinop.com (John A. Booth) Cc: questions@freebsd.org Subject: Re: Adaptect2940UW vs. BuslogicBT-958 Message-ID: <199606120953.CAA01323@MediaCity.com> In-Reply-To: <199606112218.RAA15826@ulantris.infinop.com> from "John A. Booth" at "Jun 11, 96 05:18:00 pm"
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John A. Booth wrote:
> > > one important issue is whether you really need ultrawide at all. the disks
> > > certainly can't keep up, so it only matters if you have lots of drives on the
> > > same chain, in which case you may be better off using multiple regular fast scsi
> > > controllers.
> >
> I keep seeing drives that are ultra-wide spec'd at 40 megab(it/yte?)s per
> second.
They are generally claming 40 MegaBytes per second. And, they
are also claiming 20MBs for fast-wide and 10MBs for fast. However,
all this speed exists only in the fantasy of frenzied marketing
types.
The bottomline is that:
1. Yes, they drive could possible do a short burst of data from the
drive's on board controller and cache across the SCSI bus at
10,20,40MBs.
2. But the drive can only sustain transfers from the media to host
at 0.5, 1, 2, or perhaps, if you are lucky, 3MBs per second.
There are AVI drives in the world which come with a specification that
that they can indeed sustain some certain transfer rate for their
entire capacity.
One of the limiting factors is Tcal's. Sometimes a drive will lose
track of which cylinder it is on. It then has to find its way by
moving the head to a known location and then moving back to where
it is supposed to be from there. This can take quite some time.
--
Brian Litzinger Powered by FreeBSD
<brian@mediacity.com> http[s]://www.mpress.com
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