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From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.unix.questions,comp.unix.wizards,comp.bugs.4bsd,comp.periphs
Subject: Re: /etc/disktab and RA8x drives
Message-ID: <9947@mimsy.UUCP>
Date: 24 Dec 87 12:57:09 GMT
References: <80@sickkids.UUCP>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 55

In article <80@sickkids.UUCP> mark@sickkids.UUCP (Mark Bartelt) writes:
>A few questions regarding the information in /etc/disktab (4.3bsd):  Where
>did the RA80/RA81 entries originally come from,

The stork?

>and are they even correct?

The RA81 entry is; the RA80 entry is not.

>First, let's look at the data for the RA81:
>	:ty=winchester:ns#51:nt#14:nc#1248:so:\
>I'm wondering whether it should perhaps be:
>	:ty=winchester:ns#52:nt#14:nc#1224:so:\

No, 51*14*1248 is correct, even though the disk itself is 52*14*1258.
All of the spares---that is 1*14*1248 + 52*14*(1258-1248), or 24752
sectors, or a bit over 12MB, are used in bad block replacement,
although not all of these are replacement blocks.

>... although the RA80 has 561 tracks/cylinders/whatever, only 546 of them
>are used for "real" data, yes?  [ DEC doesn't explain, in view of the fact that
>546+14 == 560, what the 561st track is used for! ]

Something like that; and, You Do Not Want To Know, or at least you are
not supposed to know.  As long as they keep it a mystery, you will have
to buy everything from DEC, right?  (Aside to DEC sales managers:  Wrong.
The more you make things a mystery, the less inclined we are to buy them
at all.  Your plan has backfired.)

>Looking back at the RA80 entry in /etc/disktab, we see:
>	:ty=winchester:ns#31:nt#14:nc#559:so:\
>
>This is truly weird.  The number of total tracks is claimed by DEC to be 561,
>and the number of logical cylinders is claimed to be 546.  So where did this
>value of 559 come from?

Thin air, as far as I can tell.  It is wrong.  If you run my driver,
the disk reports at boot time its geometry; the reported geometry is
the one that is visible to software, and the one that should appear
in disktab (or, now, on the disk label, except that you do not have disk
labels ... yet).

>Also, 31*14*559 == 242606 (same as what the disktab entry for the RA80
>uses as its Partition_C value), which is a lot more than the RA80 itself
>claims, in its MSCP packet, that it has, namely 237212 sectors.

If you have RA80s, *fix your partition table*.  The sectors that
are named by numbers >= 237212 are replacement blocks.  If you
write on them, you may change random sectors in the range [0..237211].
The tables in my driver are probably still wrong (I have no RA80s
on which to make tests).
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris