El día Friday, November 19, 2010 a las 08:51:38PM +0200, Alexander Motin 
escribió:

> > Could it be that unwritten/unformatted blocks are read as random data
> > from that USB key? Should I overwrite the full USB key from /dev/zero?
> 
> It is allowed behavior for SATA SSDs with TRIM command support. Deleted 
> blocks can be not guarantied to return any predictable or even 
> repeatable value. May be this logic could be extended to USB devices.

A cmp(1) with -l gives a file like this:

$ head -10 diff
196971771 134  34
196971797 134  34
196971833 134  34
196971845 134  34
196971849 134  34
196971875 134  34
196971901 134  34
196971945 134  34
196971955 134  34
196972210 134  34

of 2385059 lines, i.e. of 2385059 bytes which differ in the 3.8 GByte
copy; there are only a few patterns of diffs which are repeating:

$ sed 's/  */ /g' diff | cut -d' ' -f2,3 | sort -u
0 10
0 104
0 110
0 200
0 204
0 214
0 220
0 234
0 260
0 4
10 0
100 0
110 0
134 0
134 14
134 34
134 4
14 0
200 260
204 234
204 4
214 234
220 260
304 204
34 0
4 0
4 104
4 234
44 0
44 4

(the numbers are in octal). 

What does this mean? Does not look like errors, in case of random error
it whould be more caotic, or?

        matthias

-- 
Matthias Apitz
t +49-89-61308 351 - f +49-89-61308 399 - m +49-170-4527211
e <g...@unixarea.de> - w http://www.unixarea.de/
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