Dear Curtis,
Thank you very much for you email at the end of August, and particularly
the useful reference on the structure of FAT disks.
I'm sorry for the delay in replying -- I was off on my canal boat for
some of the time!
Because many people assume disks are error free, I decided to validate
my own suite of disks, that have been in use for between about three
years and fifteen years.
Six out of sixteen disks (totalling ~1.5TB) exposed errors to the IDE
interface, with a total of 170kB of bad blocks not counting the three
elderly disks that died during the prolonged validation process.
That's enough to concern me, what with frequent defragging operations
etc. that can spread the data corruption around the disk as if it was
dirt. I've summarised my findings at:
http://www.rodericksmith.plus.com/ncd/ncdTo.html?Integrity.ncd
<http://www.rodericksmith.plus.com/ncd/ncdTo.html?Integrity.ncd>
I may try to write a helper tool to coalesce the grown bad block tables
(and/or badblock lists) from the source file-system(s) and predict
their effect on the re-partitioning operation that's planned. Perhaps
even advise where to re-partition to avoid dangerous regions. I dabble
in a few software experiments like that in my retirement. Would you like
me to let you know how I get on?
You asked how bad blocks were flagged in FAT systems. A relevant
paragraph from the Microsoft site says:
There is also a special "BAD CLUSTER" mark. Any cluster that contains
the "BAD CLUSTER" value in its FAT entry is a cluster that should not be
placed on the free list because it is prone to disk errors. The "BAD
CLUSTER" value is 0x0FF7 for FAT12, 0xFFF7 for FAT16, and 0x0FFFFFF7 for
FAT32.
from
http://download.microsoft.com/download/1/6/1/161ba512-40e2-4cc9-843a-923 143f3456c/fatgen103.doc
<http://download.microsoft.com/download/1/6/1/161ba512-40e2-4cc9-843a-923%20%20143f3456c/fatgen103.doc>
Regards from
Rod Smith
r...@rodericksmith.plus.com
http://www.rodericksmith.plus.com
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