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From: terry@cs.weber.edu (A Wizard of Earth C)
Newsgroups: comp.unix.bsd
Subject: Re: 386BSD and IDE drives
Message-ID: <1992Sep24.022400.19483@fcom.cc.utah.edu>
Date: 24 Sep 92 02:24:00 GMT
References: <19posaINNp6j@disaster.Germany.EU.net> <1992Sep23.212547.15460@fcom.cc.utah.edu> <19r0h6INNp42@aludra.usc.edu>
Sender: news@fcom.cc.utah.edu
Organization: Weber State University (Ogden, UT)
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In article <19r0h6INNp42@aludra.usc.edu> eddy@aludra.usc.edu (George Edmond Eddy) writes:
>terry@cs.weber.edu (A Wizard of Earth C) writes:
>
>> I personally wouldn't buy an IDE because of geometry translation,
>>and there's one Maxtor SCSI drive, so far, in the same boat. I like the
>>UFS caching and optimization to actually result in a speedup, and it
>>can't on a geometry translated drive (see my other tirade 8-)).
>
>this would have been really cool to know before i plopped down $400
>on an IDE, i would have come up with the extra $100 for the scsi
>controller, and went with that.
>
>Does the geometry translation problem in the other triad just result
>in a loss of intended performance gains, or can it result in freaky
>things happening to files and filesystems?
The only time it acts "funny" is if the translation is used at one time
but not another -- for instance, 386BSD.
The inital program load (IPL) code is from ROM and uses BIOS -- so the
geometry translation is in effect. Later, the "real" boot loader loads
the kernel using BIOS -- still no problem. Then the kernel takes over
in protected mode -- problem. Because the kernel has a driver which
probably ignores translation (which is generally a function of the BIOS,
although not in every case, ie: the Maxtor SCSI drive), the location
for paging and so on is not the load location. In addition, you may find
that during install from a floppy that the boot information could be
written to a location on the hard disk that happened to cause it to boot...
but that the translated boot information locates to somewhere in the middle
of the untranslated disk. You will run fine until you accidently overwrite
your boot information and it "mysteriously" quits booting.
A lot of this can be alleviated by picking the user defined drive type and
entering the correct geometry as part of the CMOS setup. You of course
have to be able to *find* this information out, however.
The other common problem is when you try to "partition" the drive. Since
the master boot record and partition table are at the front of the disk,
giving 386BSD the whole disk works (because sector 0 cylinder 0 usually
translates to the same location as it's untranslated value), but partitioning
doesn't work (because the translated address of the partition is not the
same as the untranslated address because it occurs at an offset greater than
0). This is also fixed by the "user defined drive type" fix.
The problem with the "user defined drive type" fix is that you probably
wouldn't be doing geometry translation unless you needed it... which means
more than 1024 physical cylinders on a drive (anyone ever wonder why MFM
disks can only have up to ~130M on them? No geometry translation to let
them pretend that they have 1024 or less cylinders).
Geometry translation is DOS's way of breaking the 1024 cylinder boundry...
beware of large drives that let DOS use the whole disk!
Since DOS can't access cylinders past 1024, this means a DOS partition
would have to be before that -- thus either reducing the usable disk space,
or making the 386BSD partition the second one rather than the first. A
problem in asboot.c means that not having the 386BSD partition first can
mean it won't work.
One of the most hilarious presentations I ever sat through was by a company
that tried to sell us "disk optimizer" software to "make the files
contiguous for faster access, reduce seek time, and practically eliminate
delays from rotational latency" -- right after selling us machines with
IDE drives in them. Since they were for DOS, I really didn't care of the
drives were IDE or not. My problem was with the company: either they were
stupid or they thought we were, either of which is reason enough to not do
business with them again.
Now I wouldn't buy an IDE drive at all, since I expect to eventually install
386BSD on all machines in unlocked offices. 8-). 8-).
Terry Lambert
terry_lambert@npd.novell.com
terry@icarus.weber.edu
---
Any opinions in this posting are my own and not those of my present
or previous employers.
--
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