Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!pacific.mps.ohio-state.edu!linac!mp.cs.niu.edu!bennett
From: bennett@mp.cs.niu.edu (Scott Bennett)
Newsgroups: comp.sys.next
Subject: Re: SR2.0 BuildDisk vs SR2.1BuildDisk
Message-ID: <1991Apr24.023556.24667@mp.cs.niu.edu>
Date: 24 Apr 91 02:35:56 GMT
References: <009472C9.1FEB89E0@UAVAX0.CCIT.ARIZONA.EDU> <1490@toaster.SFSU.EDU>
Organization: Northern Illinois University
Lines: 65

In article <1490@toaster.SFSU.EDU> eps@cs.SFSU.EDU (Eric P. Scott) writes:
>NeXT cleaned out /etc/disktab in 2.1--all the SCSI disks that
>were listed in 2.0 are GONE.  Only the OD description remains.
>
>  [text deleted  --SJB]

     Thanks a *bundle* for the warnings!  If I ever manage to get my
hands on 2.1, I'll remember to save /etc/disktab somewhere.
>
>Here's what scsimodes displays:
>
>SCSI information for /dev/rsd1a
>Drive type: FUJITSU M2266S-1024
>1024 bytes per sector
>45 sectors per track
>15 tracks per cylinder
>1658 cylinder per volume (including spare cylinders)
>3 spare sectors per cylinder
>15 alternate tracks per volume
>1113503 usable sectors on volume
>
>So the "raw" geometry is
>  1658 cylinders * (45 sectors/track * 15 tracks/cylinder)
>= 1658 cylinders * 675 sectors/cylinder
>= 1119150 sectors
>
>But that doesn't agree with The Bottom Line.  Let's take a closer
>look at those numbers.  The 15 alternate tracks at 15 tracks per
>cylinder add up to one complete cylinder, so there are only 1657
>usable cylinders.  With 3 spare sectors per cylinder, there are
>only 672 sectors left--what's 1657*672?  1113504.  Why does
>scsimodes show one less?  I think it's an error; if you do
>scsimodes -v  that number turns up as "last logical block"--*not*
>the number of blocks (which does show as 1113504).  So how many
>blocks are available for filesystem use?  1113344.  You have to
>figure in the 160 blocks for the front porch too.
>
     My guess is that the missing track is assumed to be the
boot blocks.  I don't know what exactly you mean by "front porch,"
but I'm assuming that it is stuff that is operating system-dependent,
e.g. disk volume label, partition map, bad sector/track information,
available alternate track locations, etc.  All operating systems
can be expected to need some sort of boot program and the computer
will always need to be able to find it in the same place (e.g. track 0),
but the rest of the stuff could vary according to the software.

> [remainder of text deleted  --SJB]
>
>
>					-=EPS=-


                                  Scott Bennett, Comm. ASMELG, CFIAG
                                  Systems Programming
                                  Northern Illinois University
                                  DeKalb, Illinois 60115
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* Internet:       bennett@cs.niu.edu                                 *
* BITNET:         A01SJB1@NIU                                        *
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*  "Spent a little time on the mountain, Spent a little time on the  *
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*  since 25 Sept. 1970!!!  Yippee!!!!  Wondering what's NeXT... :-)  *
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