mkfs and 80SC interleaving

[Dave Wells]

In article <42900002 at m.cs.uiuc.edu> coolidge at m.cs.uiuc.edu writes:
>
>We've got several Apple 80SC's (external and internal) used for A/UX
>in our lab. Recently we set up one of the Macs as an NFS server for
>the rest of them and reformatted a previously MacOS drive as a second
>A/UX drive. The new drive's performance seems to be really bad, and it
>seems to be doing far too much seeking. I suspect that by using the m
>and n (interleaving) parameters with mkfs the performance could be
>greatly improved.
>
>Does anyone know the "right" interleaving numbers for an internal (or,
>for that matter, an external) 80SC, especially one used mostly as
>an NFS-mounted server drive?

There are several things that can affect your hard drive performance.
>From top to bottom: (or bottom to top, if you like.)

o What interleave was it formatted with.  Did you originally initialize
  it with HD SC Setup on a Plus or SE?  That'd hurt (not much, but some).
o When you used mkfs to create your file systems, did you allow it to
  use the defaults?  If so that'd hurt lots.  As is documented, the
  defaults are 7 for the gap and 400 for the "modulo operator."  A gap
  of 1, 2 or 3 will produce very similar results while 7 is like
  pouring molasses into the drive.  After talking to bunches of people
  I've discovered that few know much about the thing called the
  "modulo operator."  What I'm pretty sure you should use is the
  cylinder size (in blocks).  For a good (?) old ST225 with 4 heads
  and 17 sectors per track that'd be 68.  (4*17)  The quantum drives
  I think are different in that they don't have a fixed number of
  sectors per track.  They start at 28 in the center and end up
  with 35 at the outermost tracks.  With 5 heads this works out to
  either 140 or 175.  In testing I couldn't find much difference
  in timings, but I don't know if this would change with heavy
  usage (fragmentation).  Try a gap of 1 and modulo of 140.  See if
  that helps any.
o Do you have enough NBUFs?  Is the system being used heavily now so
  that all drive accesses seem slower or are just the new drives dogs?

Hope this helps.

-Dave

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           Dave Wells, Apple Computer, Inc.  MS: 37-O  (408) 974-5515
        Internet: dwells at apple.com or AppleLink d.wells or GEnie D.WELLS
 These opinions may be nothing more than the ramblings of a fatigued tinkerer
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 There's one big difference between genius and stupidity.  Genius has limits.
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