This is why you don't trust a single backup and why you verify your backups.

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dmitche3

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May 25, 2008
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I am very careful about backing up my data and here is a good case as to not rely on a single backup.

I read an article the other day about 'bit rot' and it got me to thinking that I have not been a good admin of late. While I back up my data (personal PC only) to two back up drives I haven't done a bit comparison on any of the back ups in over a year.

So I started to do bit comparisons and sure enough two videos ( so far ) have chunks corrupted. One was only a single byte, the other had a chunk 0x7000 bytes long that looked like assorted programs, error messages,etc. (not a virus).

While I probably won't have lost this video from some time yet to come, in the I would have only the corrupted version that was on my main hard drive and my one backup drive. :(

Being a system admin off and on for nearly 30 years I'm embarrassed to have forgotten such a fundamental step of verifying my backups. lol
 
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Thanks for the information as many people are going to want to know how to do file comparisons without spending money on tools.
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Paperdoc

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I fully support what OP has said. I vividly remember a story that illustrates how old this dilemma is. It took place about 1970 in the mainframe operations of a small university. The mainframe was an IBM System 360 / 50. A junior programmer made a couple bad mistakes and ended up wiping out all the files on all the disk packs on a Friday afternoon. Time for the backup tapes to restore from. BUT the OS could not read the backup tapes!! The tapes had been made and stored properly, but apparently the backup code wrote the tapes with a few errors so they could not be read back in! The staff went to work over the weekend and built a list of possible fixes to apply to the machine-coded reading routines. Another junior programmer got lucky and his patch worked the first time. It took most of the weekend to restore from the tapes, but they were entirely successful.

The most amazing thing we all considered was that the OS being used on the system had been in wide circulation on mainframe systems in North America for nearly a year, and NOBODY had ever sounded an alarm that the backup tapes it made could not be read!
 
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popatim

popatim

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for a couple of files a command prompt will do: fc /b file1 file2
for large files: vbinDiff works well

I use Integrity Checker on my WHS11 server.
 
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dmitche3

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I verify my backups using Beyond Compare. I use it to backup also as it does drive,folder, or file comparisons and a lot more. I primary used it before for code comparisons as the 'diff' feature is great.

Beyond compare has a 'compare' option that does a bit for bit comparison. When comparing folders the tool only checks for the obvious differences (size, dates, etc) but then you select folders or files to compare.
 
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dmitche3

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I only had a few memories of working on the 360/370's. :) I was mainly a Burroughs guy who moved into Unix sys 3 and ....
I remember those lovely 9-tracks and how at the university that I worked we maintained a master and 3 backups. When ever we did an update we created a new master and did a verification on it immediately. If it failed I would take the tape to the cleaning unit, clean it, and put the tape back into the unused rack after dating it that it failed. Some number of failures later the tape would be tossed and some people took them and sliced them down to use on their reel to reel players. I never could do that as I didn't know how to splice the tape, nor the equipment.

I also remember when I worked for a very big and famous hospital the surprise when they went to reboot their VAX VMS box and the tapes were no good and it wouldn't reload. :(
 
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dmitche3

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Thanks for the information as many people are going to want to know how to do file comparisons without spending money on tools.
 
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Y0GI

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I verify my backups using Beyond Compare. I use it to backup also as it does drive,folder, or file comparisons and a lot more. I primary used it before for code comparisons as the 'diff' feature is great.

Beyond compare has a 'compare' option that does a bit for bit comparison. When comparing folders the tool only checks for the obvious differences (size, dates, etc) but then you select folders or files to compare.
Click to expand...

Thank you, Dmitche3!

Yogi
 
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