Newsgroups: comp.periphs.scsi
Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!uunet!xstor!iverson
From: iverson@xstor.com (Tim Iverson)
Subject: Re: How much faster is a 16 bit SCSI Ca
References: <396@oiscola.Columbia.NCR.COM> <283400133@adaptx1>
Organization: Storage Dimensions, Inc.
Message-ID: <1991Jun03.192718.12054@xstor.com>
Date: Mon, 03 Jun 91 19:27:18 GMT

In article <283400133@adaptx1> neese@adaptx1.UUCP writes:
>>Under Windows 3.0, you will notice a (perhaps significant) decrease in
>>transfer rate if you go to a bus-mastering controller due to the double
>>buffering used to work around the physical-to-virtual translation.
>
>Nope. [...]
>Prior to the VDS services, one had to do double buffering and hope no
>other program relocated the driver and buffer.

I was aware of this, but I didn't know that the Adaptec driver actually used
this method - which, of course, is obviously far preferable to the
double-buffering hack required before virtual-to-physical translation was
available.

>>flawless image of the media.  Some drivers, like the ones we sell with our
>>products :-), are smart enough to remap defects on-the-fly, so you'll never
>>even see one until you run out of spares.  Reformat and you can gain a new

>Or you can have the drive do the actual remapping.  Some of the higher end
>drives support this, but have it turned off.  One can also setup the error
>page to have the drive recover all the data it can before remapping the
>suspect sector.

This is true, but all is not roses.  Consult your OEM manual very carefully
before relying on this method.  An example: the Wren VI HH says it supports
AWRE (automatic write reassign enable), but if you read closely, you'll see
that it only reassigns if the header is corrupt - this means that the data
could be bad (and the drive might know this if you do a write with verify),
but it won't reassign.  Erasable optical drives have similar problems.

Of course, if you're using a driver that does not support recovery, then
AWRE (or even ARRE) is your only recourse.

>			Roy Neese
>			Adaptec Senior SCSI Applications Engineer
>			UUCP @  neese@adaptex
>				uunet!cs.utexas.edu!utacfd!merch!adaptex!neese

- Tim Iverson
  iverson@xstor.com -/- uunet!xstor!iverson