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Date: Mon, 15 Jul 1996 06:14:07 +1000
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199607142014.GAA05013@godzilla.zeta.org.au>
To: joerg_wunsch@uriah.heep.sax.de, julian@ref.tfs.com
Subject: Re: Jaz drive questions
Cc: Stephen.Couchman@imagenet.on.ca, freebsd-questions@FreeBSD.org,
        freebsd-scsi@FreeBSD.org, n_melhor@Telebit.COM
Sender: owner-questions@FreeBSD.org
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>> > >  sd1(ahc0:2:0): ILLEGAL REQUEST asc:24,0 Invalid field in 
>> > >  CDB sd1 could not mode sense (4). Using ficticious 
>> > >  geometry 1021MB (2091050 512 byte sectors)
>> > 
>> > This means that FreeBSD _did_ recognize the drive.  Iomega apparently
>> > didn't bother to implement the SCSI mode sense command, so the driver
                               ^mode page 4 of the
>> > can't determine anything about the number of heads or sectors/track
>> > on the disk (if any).
>> ...
>the geometry is in fact unimportant..

It's important for booting.

>the ficticious one should work just fine..

Only insofar as it is not much used, or happens to match the geometry
used in the MBR.  If there is no MBR and you use the (64 heads) * (32
sectors) geometry then booting will only be possible provided:

1) The SCSI BIOS supports this geometry either as a default or by
   interpreting the MBR.  It probably does.
2) The boot cylinder is < 1024.  Each cylinder is 1M in the 64x32
   geometry, so there is no problem for drives smaller than 1024MB.
   The drive under discussion is slightly smaller so there is no
   problem for it.

A geometry of (255 heads) * (63 sectors) should be used for drives in
the 1GB-8GB range if the SCSI BIOS supports it.

>> The claimed number of sectors looks highly suspicious: it's IMHO
>> 10 x too large.

It's normal for a 1GB drive.

Bruce