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From: jesup@cbmvax.commodore.com (Randell Jesup)
Newsgroups: comp.sys.amiga.hardware
Subject: Re: Problems with hard drive
Keywords: A2000HD, A2090A, SCSI, Wren IV, prep, "Not a DOS disk"
Message-ID: <17931@cbmvax.commodore.com>
Date: 22 Jan 91 21:30:41 GMT
References: <1615@contex.UUCP>
Reply-To: jesup@cbmvax.commodore.com (Randell Jesup)
Organization: Commodore, West Chester, PA
Lines: 52

In article <1615@contex.UUCP> brian@contex.UUCP (Brian Love) writes:
>I am having trouble connecting a CDC Wren IV (344Mb SCSI) hard disk to my
>A2000HD (see below for full system configuration).  The documentation for
>the Wren indicates very clearly the drive has 1549 cylinders, and (fairly
>clearly) 9 data heads.  The docs are not clear on BlocksPerTrack; by some
>simple arithmetic, the drive must be able to support at least 50 512-byte
>blocks per track.  Of course, that configuration doesn't work.

	Hopefully someone has attached one of these before, and will mail
you or post.  Don't forget that SCSI drives often reserve some number of
cylinders and some number of sectors per track or cylinder.  BTW, 50*512*
1549*9 is 356Meg, at least by one definition of "meg".  Also, the stated
size may well include spare cylinders and sectors.  You need to find out
the number of formatted data blocks (logical blocks) available with 512 byte
sectors.  This should be available from the manufacturer.  More modern
controllers have ways of asking the drive for that information directly.

>When connecting a Vertex (80Mb ST-506) drive, I discovered that the prep
>program does not like initializing disks with more than 7 or 8 surfaces
>(the Vertex drive has 10).  I found I could get around this by telling prep
>the disk has only 7 surfaces, but telling mount the real number of
>surfaces.  To accomodate for this, I also have to lie to prep and tell it
>the disk has more cylinders than it really has.  For the Wren,
>1549cyls/50bpt/9surf would map approximately to 1991cyls/50bpt/7surf.  Of
>course, that solution doesn't completely work either.

	The 2090(a) doesn't support more than 8 heads for st506 drives.  This
has no affect on SCSI.

>I've been able to get 4 partitions to work, using approximately 240Mb of
>the disk.  The 5th partition invariably fails.  I don't trust all 1549
>cylinders after the prep nonsense, so I create 1 partition from cyl 4 thru
>cyl 1549 (or higher).  The format of this partition always fails on
>cylinder 1402.  So I say, fine, I'll run my partitions up to cylinder 1400
>and that'll give me 307Mb.  And, of course, that doesn't work either.  The
>fifth partition will format all cylinders up to 1400, but I get a requester
>saying "Not a DOS disk - Unit 6".

	I seem to remember some problem with 2090's and very large SCSI
drives (very large for the time it was designed, back around 86 or so).
There may be some size limit at which a bug is hit.  I'll ask Steve Beats 
about it, he knows more about it than I do.  Also, at least some versions
of FFS had bugs with partitions of 300+meg.  I think these are fixed
in 1.3.2 or maybe 1.3.3 (they certainly are in 2.0, though in 2.0 to 2.02
it had a 500Meg partition size limit, that's been fixed since then).

-- 
Randell Jesup, Keeper of AmigaDos, Commodore Engineering.
{uunet|rutgers}!cbmvax!jesup, jesup@cbmvax.commodore.com  BIX: rjesup  
The compiler runs
Like a swift-flowing river
I wait in silence.  (From "The Zen of Programming")  ;-)