mkfs interleave factors

[Rick Auricchio]

Just a quick note on what to use for the mkfs parameters for "gap" and
"blocks/cyl".  Use 1 and 1.

My tests have verified the observation that things are markedly slowed down
by the bogus defaults of 7 and 400.  I'm now changing those defaults to 1 and 1
for a future (post-1.1) release.

Use of 1 & 1 works fine on the drives I have here; Quantums have partial and
full-track buffering, hence they work well at 1-1 interleave.  Seagates don't
have onboard buffering, but A/UX 1.1 makes the 1-1 physical interleave anyway
with the Vulcan I/O acceleration code.

A/UX 1.0 may not be optimal with 1 & 1; it's possible that some interleaving
of filesystem blocks makes sense, but I haven't tried it.  I think it's better
to make the file system "right" so that it isn't horrible after an upgrade.

BTW, mkfs divides the "gap" value by 2 to get 512-byte blocks.  That makes
a gap of 1-3 become 1; 4-5 become 2; 6-8 become 3, etc.  Even dumber.

In conclusion, just use 1 & 1 for "gap" and "blocks/cyl".  This even improves
floppy performance by >2x.
-- 
Rick Auricchio, Apple Computer Inc, 20525 Mariani Av MS 27AJ Cupertino CA 95014
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