Xref: utzoo comp.unix.aux:571 comp.sys.mac:24771 comp.periphs:1441
Path: utzoo!utgpu!attcan!uunet!portal!cup.portal.com!ts
From: ts@cup.portal.com (Tim W Smith)
Newsgroups: comp.unix.aux,comp.sys.mac,comp.periphs
Subject: Re: A/UX generic SCSI driver and Syquest 44Mb removable drives
Message-ID: <13236@cup.portal.com>
Date: 6 Jan 89 11:54:17 GMT
References: <4370@portia.stanford.edu> <40443764.1285f@maize.engin.umich.edu> <eakdo#+=michael@xanadu.COM>
Organization: The Portal System (TM)
Lines: 19

It's not nice for a driver to save pointers if the drive hasn't
told it to.  Consider a high performance drive that transfers
data directly from the disk to the SCSI bus.  In most cases,
this will not cause any problems.  However, suppose an error
occurs that the ECC fails to correct.  The drive will have to
try to re-read the data off the disk.  This could take a while,
so the drive might disconnect, then reconnect when it has
finished re-reading the data.  Since it has not issued a
SAVE DATA POINTERS, it expects the data it sends to overwrite
the bad data it previously sent.

If the driver assumed that the drive just "forgot" to issue
a SAVE DATA POINTERS command, this won't work.

I don't know if anyone has tried this trick of sending bad
data and then overwriting it with a disk drive, but I believe
that there are tape drives that do this.

					Tim Smith