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Path: sserve!manuel!munnari.oz.au!mips!mips!darwin.sura.net!Sirius.dfn.de!zrz.tu-berlin.de!gmdtub!bigfoot!tmh From: tmh@doppel.first.gmd.de (Thomas Hoberg) Newsgroups: comp.unix.bsd Subject: Re: SCSI driver bug when accessing DOS partition Message-ID: <TMH.92Aug20013232@doppel.first.gmd.de> Date: 19 Aug 92 23:32:32 GMT References: <1992Aug19.020535.2080@noose.ecn.purdue.edu> Sender: news@bigfoot.first.gmd.de Organization: GMD-FIRST, Berlin Lines: 36 In-reply-to: tgt@neon.ecn.purdue.edu's message of 19 Aug 92 02:05:35 GMT In article <1992Aug19.020535.2080@noose.ecn.purdue.edu> tgt@neon.ecn.purdue.edu (Conan the Librarian) writes: I ran across the following Adaptec driver bug when attempting to configure mtools to read an 80 Mb DOS partition d:, which is on a SCSI disk. The problem: the SCSI driver routine asstart (in the file /sys/i386/isa/as.c) fails with the message "out of range, cannot happen?" (due to nscatter==NSCATTER, which means nothing to me!!). This subsequently causes the disk_read() routine of mtools (in the file buf_read()) to fail, printing the message "disk_read: read: Device not configured" This is not a bug but simply a limitation of the current SCSI driver. The Adaptec allows you to bundle a couple of reads together in a scatter list. The hardware maximum size for this list is 16/17 entries per mailbox. Since the Intel CPUs have a 4k page size at most 16 pages of 4k can be read with a single command (64k). At a 2k cluster size DOS allocates twice as many sectors for the FAT as there are megabytes in the partition. With partition sizes greater 64MB the fat_read() routines requests a read of more than 64k which then failes with that warning. There are several workarounds: 1) use the block device (slow, but the easiest) 2) hack mtools to do it's own buffering (some work) 3) use a bigger cluster size for your DOS partition (more wasted disk space) Of course the best thing would be to enhance the Adaptec driver to support command chaining (even more work). There is a new Adaptec driver by Julian Fletcher (sp?) under evaluation, maybe that will fix the problem. --- Thomas M. Hoberg | Internet: tmh@first.gmd.de 1000 Berlin 41 | tmh@cs.tu-berlin.de Wielandstr. 4 | Germany | BITNET: tmh@tub.bitnet +49-30-851-50-21 |