Off Topic: how do you ensure your file backup operations are not corrupt? (windows xp)

Doug Franklin jehosephat at mindspring.com
Thu Jul 29 16:02:54 EDT 2010


On 2010-07-29 13:55, Sam L wrote:
>      When I try to open the jpg using "windows picture and fax viewer"
> I get a blank screen and
>      either "generating preview" or "drawing failed".  When I use
> "microsoft office picture viewer" I just get a black screen.
>      And hey ... that's odd ... when I use "internet explorer" the file
> actually seems to display.  Strange!

That potentially points toward something in the file formats that aren't 
being interpreted consistently among the different viewers, or something 
that's missing that some viewers can/will default and others won't, or 
they try but use a default value that doesn't work with these particular 
files.  JPG files are very sensitive to even small corruptions in the 
data stream due to the progressive nature of the encoding.

One way to get around it might be to open them in the program that can 
open them, and save them in that program, too.  That might "fill in the 
blanks" that are causing problems for the other programs.  Of course, 
you risk having another round of lossy-compression-degradation in the 
quality of the JPGs.

>      Backup has been either a simple copy/paste using windows explorer
> or by "syncback" which is a pretty decent
>      free backup software.  File by file comparisons doesn't really
> sound realistic or practical, except for maybe once a year.
>      I have currently 15,000+ files.

15,000 files will take at most a few minutes to check on most modern 
computers using an external USB 2.0 or Firewire drive, less for an eSATA 
drive.  And even if it takes longer than that on your computer, kick off 
a backup Monday night when you go to bed, and a verification Tuesday 
night when you go to bed.  It'll be done in the morning.

>      I just check my syncback software and there is a "verify" option
> which I will use from not on at the very least.
>
>    If it ain't verified, it ain't a backup.  Trusting that they were OK
> may be part of what got you in this mess.

OK, I didn't make my meaning clear there.  Like someone else said 
earlier today, the only way to verify a backup is to restore it and 
actually use the restored files.

Now that I think about it, this actually might be a case where it would 
be a useful project, but still a small enough one that I could get it 
done, to create some Linux shell scripts and/or Windows "batch" files to 
do some of these operations.  Say, one to do the backup, one to do the 
restore, and one to test the restored files.

The easiest way for you to test your backups without writing scripts or 
programs would be to have another external drive that's doesn't hold 
anything else.  Fast format that drive, copy the backed up files to it, 
then use a free "duplicate file finder" utility to confirm the restored 
files are the same as the backed up files.

-- 
Thanks,
DougF (KG4LMZ)




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