[net.micro.mac] HD20 error handling at boot

borton@sdcc3.UUCP (Chris Borton) (01/25/86)

Can anyone explain what the HD20 does upon boot after a crash?  Depending
upon the situation before "the bomb" it will take 2-3 times longer before it
ejects the floppy.  During that time some intensive hard disk stuff is going
on.  Everything always turns up fine, but I'm curious what it's doing.  It's
particularly bad recovering from Switcher with 2-3 applications.  (Gee, I
wonder why? :-) )

--Chris
-------------
Chris Borton, UC San Diego Undergraduate CS	
Micro Consultant, UCSD

borton@ucsd.ARPA     or  ...!{ucbvax,decvax,noscvax,ihnp4,bang}!sdcsvax!borton

darin@ut-dillo.UUCP (Darin Adler) (01/28/86)

<

> Can anyone explain what the HD20 does upon boot after a crash?  Depending
> upon the situation before "the bomb" it will take 2-3 times longer before it
> ejects the floppy.  During that time some intensive hard disk stuff is going
> on.  Everything always turns up fine, but I'm curious what it's doing.  It's
> particularly bad recovering from Switcher with 2-3 applications.  (Gee, I
> wonder why? :-) )

As explained to me at the developer's conference by Scott Knaster:

	The HFS file system maintains a bit map that determines which
	sectors on a disk are free and which are used.  (This in addition to
	a "extents file" that determines where each file is stored.)  When a
	system crash occurs, some sectors may be marked as used, even though
	they are unused, and vice-versa.  When a volume is mounted, if it
	was not properly Unmounted/Flushed the last time it was used, a
	"scavenge" routine runs, determining which sectors are used/unused.

This was nice to hear, because before using HFS, my Corvus volumes would
gradually lose sectors until I had to re-format them.
-- 
Darin Adler	{gatech,harvard,ihnp4,seismo}!ut-sally!ut-dillo!darin

"Such a mass of motion -- do not know where it goes"	P. Gabriel