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From: hamachi@KIM (Gordon Hamachi)
Newsgroups: net.micro.mac
Subject: Bad Disk Block Horror Story
Message-ID: <8601030325.AA25594@kim>
Date: Thu, 2-Jan-86 22:25:58 EST
Article-I.D.: kim.8601030325.AA25594
Posted: Thu Jan  2 22:25:58 1986
Date-Received: Fri, 3-Jan-86 08:22:23 EST
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: University of California at Berkeley
Lines: 61

I just found out that a disturbingly large number of my floppy disks have
bad blocks.  Using the ScanDisk utility, I tested all 131 of my disks and
discovered 7 with blocks that couldn't be read.  But wait, it is worse than
it looks.  Two of 17 "work disks" were bad, and 5 of 59 "archive disks"
were bad.  55 other disks came from Apple's software supplement, and have
never been touched.

But wait again, it is worse yet.  Many times I've had to scavenge and
reformat disks when they've been trashed such that "Some files couldn't
be read and were skipped", "This disk is unreadable.  Do you want to
initialize it?", or "The file copy didn't work.  Try copying to a different
disk".  The bad ones were ONLY the latest ones I've found.

But wait one more time, it is again worse!  There are likely many more bad
disks in my collection.  Further checking shows that many of the errors are
"soft".  For each bad block on each disk I list the number of times (out of
10) it couldn't be read.  For example, for disk 6 in 10 trials there were
29 bad block reads distributed over 3 different blocks.

Disk   Times each block was bad in 10 trials
1	3, 4, 10, 9, 9, 2, 1
2	2, 1, 1
3	10, 3, 7, 3
4	10
5	8
6	10, 10, 9
7	2

I don't think I'm the only one with these problems.  Just about everyone I
know with a Mac sooner or later finds himself with a file or disk that is
corrupted.

You too probably have a fair number of disks that are screwed up.  No?
You probably just don't know it yet.  Macintoshes seem to suffer from this
problem with distressing regularity.  Why? What could cause this?  I've never
had such disk problems with IBM PC disks.

Some possibilities:
1. Program bug
2. Finder bug
3. Power glitch or other "act of god"
4. External magnet, x-ray, etc
5. Bad disk medium
6. Physical daage to disk
7. Bad disk drive
8. Bad disk drive design
9. User error (turning off power during a disk write, etc)

I urge you all to check every one of your disks.  If you would mail your
findings to me, I will summarize the results.  Please report:

   1. The number of bad disks you find, broken down according to the amount
      of use each is given.
   2. How long have you had your Mac?
   3. Estimate the number of bad disks you've encountered during this time.

Also, can anyone explain why these problems occur?

Gordon Hamachi
(E-Mail: ucbvax!hamachi, hamachi@berkeley.edu)
(USMail: Computer Science Division, Evans Hall, Univ. of Calif, Berkeley 94720)