david@walking.pub.uu.oz.au (David Le Blanc) (12/15/90)
I have just prepped/formatted my A590 internal harddrive, and copied about
16 Meg from my second drive. Now, when I type 'cmp all hd0: dh0:' it shows
that *TWO* files are corrupt. By all coincidence I have *TWO* bad blocks
on the drive. (Which *appear* to be mapped out properly..)
I ran a sector editor, and traced the corrupt files. It seems that both
hit *BAD* blocks, and when they do, the drive zips a fair way (from the
noise it makes) and reads a different block. (probably what the corrupt
block is mapped to?)
Now, doing a '*verify* disk' turns out the following info
'bad block recovered at 39434 (track 730, sector 2 head 0 block 39422)'
'bad block recovered at 39488 (track 731, sector 2 head 0 block 39476)'
Now judging from these mappings, I wouldnt expect the drive head to have
to move at all to reach the remapped sectors.
Now, in ALL cases of corruption, the file had *ONE* block replaced with
that from another file that was copied on AFTER.
The conclusion?
For each BAD block, the data is written to the WRONG place entirely, and
eventually written OVER by files written later to the disk, since the
block that the data *IS* eventually written to, is not allocated in the
bitmap.
What I would like to know (as well as how to fix this stupid problem)
is how a bad blocks handled (when handled properly). I find it hard to
believe all bad blocks are mapped to somewhere else on the disk, because
you would run out of room! And if the bad block is marked in the bit map
as a bad block, is it then a file system record? or does the drive
keep record of the bad blocks? and if so, where? (after all, its all taken
up for data!, except the first two blocks used by the file system..)
basically, HELP!
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David Le Blanc UUCP (home) : eyrie!walking!david@labtam@munnari.oz
david@walking ACSNET (work) : david@dogmelb.dog@munnari.oz
CSIRO Division of Geomechanics
"Life? Dont talk to ME about life.. " : Marvin the paranoid android.
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