Disk geometry and /etc/disktab

[Matthias Urlichs]

In comp.unix.aux, article <2698 at dftsrv.gsfc.nasa.gov>,
  jim at jagmac2.gsfc.nasa.gov (Jim Jagielski) writes:
< The characteristics of a disk drive's geometry needs to be included in A/UX
< 2.0 /etc/disktab file.
Side question: Are these values used for anything, or are they just there for
performance reasons (mkfs for a BSD file system)?
Why can't these utilities pretty please _ask_ the SCSI drive, instead of
pestering us poor clueless users with maintaining that stuff?
And what, if anything, are we to do with drives which have a variable number
of sectors (depending on the track)?

< There are two ways of getting this information: either
< from SCSI Evaluator OR LaCie SilverLining.
< 
< My trouble is that both return DIFFERENT values for the number of cylinders
< for all my hard disks. Which should I believe? For example, for my Quantum
< 80 (the newer 3 1/2 inch) SCSI Eval. returns 834 cylnders, whereas SL returns
< 837 (and 6 heads, 32 sectors/track)... (SL is 5.24/09 and SCSI Eval is
< both 1.00 and 1.03)
< 
It seems that SilverLining includes the spare sectors.

Since the SCSI drive doesn't make these available to ordinary mortals (or
ordinary file systems), you probably should believe SCSI Evaluator.

Disclaimer: Anything I said could be wrong.

-- 
Matthias Urlichs -- urlichs at smurf.sub.org -- urlichs at smurf.ira.uka.de
Humboldtstrasse 7 - 7500 Karlsruhe 1 - FRG -- +49+721+621127(Voice)/621227(PEP)