[Info-vax] Backup/physical question

[Stephen Hoffman]

On 2015-03-16 02:47:19 +0000, JF Mezei said:

> It appears that bad blocks on diskette in a backup/physical do not 
> result in the block being filled with 0s.

The contents of the bad blocks are read and returned to the caller, 
errors and all.  This allows more advanced users to potentially locate 
and repair the damage.  That the data is unreliable is generally 
flagged until the sector is revectored and rewritten, though not all 
hardware has that support.  Floppy disks don't support much in the way 
of error detection or error recovery, and don't support revectoring.  
Worse, some ECC is pretty weak, and can miss multiple-bit errors.  q.v. 
rowhammer with single-bit correction, double-bit detection.  Flip more 
than two, and weak ECC might be blind to it.

<http://labs.hoffmanlabs.com/node/1115>
<http://labs.hoffmanlabs.com/node/838>


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