Images - Verification or Testing for Backup

Discussion in 'backup, imaging & disk mgmt' started by beethoven, May 18, 2008.

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  1. Huupi

    Huupi Registered Member

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    WOW thats quite comprehensive,i take experts findings seriously.Good work !

    But like Long View not to bother with verifying i keep images on different external disks. ;)
     
  2. markymoo

    markymoo Registered Member

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    Overall based on those statistics alone it be sensible to use the verify for the majority that use backup software. The risk goes up when you not computer savvy.

    Yes a checksum error is more common because just 1 byte of data changes means a different checksum. Certain image software do error checking some better than others.

    If the data is so so important to you that you can not afford to lose it then why not use the verify anyway as a extra check. The extra time is worth it over the alternative of an increased risk of lost data. If the data is not so important such as imaging system partitions that don't have personal data then don't bother with the verify.
     
    Last edited: May 22, 2008
  3. MrBrian

    MrBrian Registered Member

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    If you make separate backups often and keep at least a few older backups, then I would agree that it's reasonable to skip verification, provided that you've successfully tried a verification (or restore, which does a verify automatically) a few times from your restore media with the current version of your restore program. For added confidence that silent corruption hasn't become a common problem, you could also occasionally do a verification (or restore, which does a verify automatically). On the other hand, if you backup infrequently, or don't keep older versions of backups, or have high value data, then IMHO it's more important to verify after every backup.
     
    Last edited: May 23, 2008
  4. MrBrian

    MrBrian Registered Member

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    Thank you :). I learned from these articles also.
     
  5. MrBrian

    MrBrian Registered Member

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    Some results I didn't mention previously are found here.

     
    Last edited: May 23, 2008
  6. MrBrian

    MrBrian Registered Member

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  7. Long View

    Long View Registered Member

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    I don't agree with his conclusions.

    1." I should do incremental.." I have full data backups going back to 1996
    2. "having 2 corrupt is not better than one"

    some years ago I found a few data files were corrupt. The culprit turned out to be exec software. It had corrupted several thousand images in a database. Fortunately they were all in the letter B folder. I looked at a one month old back up and they were the same. I looked at older back ups and eventually found clean files which I restored. I still have these full images and backups. I think the problem here is that people have one small backup drive and replace one image or backup with another - very dangerous. The solution is simply to have multiple backups on different media in different locations
     
  8. Huupi

    Huupi Registered Member

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    My vote ! :thumb:
     
  9. Peter2150

    Peter2150 Global Moderator

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    I thought it was a kind of dopey article, suggesting solutions based on not knowing what happened. Incrementals by nature are more apt to be a problem then a full image(not that I've had a problem).

    But if you have a corruption problem, first thing is to narrow the source down. Should be obvious, noo_O
     
  10. MrBrian

    MrBrian Registered Member

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    I should have mentioned that to recover from latent sector errors in backup files, in conjunction with one of these programs, you might also need a program such as Roadkil's Unstoppable Copier that can copy parts of corrupt files.
     
  11. Long View

    Long View Registered Member

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    I can't comment on the others but a few years ago I took a Taiyo Yuden DVD and scratched it, left it in water for a few days, left it in the sun for a few days and so on. Using the basic DVDisaster I was able to restore until I did so much damage that the program just gave up. A very impressive program.
     
  12. ErikAlbert

    ErikAlbert Registered Member

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    This is indeed a very interesting verification method. I already downloaded DVDisaster to test my Verbatim DVD's. :)
     
  13. MrBrian

    MrBrian Registered Member

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    Just a note to those who may not know: DVDs already use the same general error encoding method as Dvdisaster, QuickPar or ICE ECC. However, using Dvdisaster, QuickPar, or ICE ECC makes the error recovery on a DVD even stronger. You can also use QuickPar or ICE ECC to protect files on a hard disk. Hard disks use an error detection and recovery method that's local to particular sectors, and thus can also benefit from QuickPar or ICE ECC.
     
  14. MrBrian

    MrBrian Registered Member

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    Correction to my own statement: after further research, it seems that remapping of iffy sectors happens only on a sector write, not on a sector read.
     
  15. RobertB

    RobertB Registered Member

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    What boot corrector utility do you use with TI? (The only one I've heard of comes with Paragon DB.)

    Robert
     
  16. RobertB

    RobertB Registered Member

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    Do either of these programs run from both within Windows and from a startup CD?

    Do either of them provide the option of both a sector-by-sector copy as well as a "normal" copy?

    I would imagine that verifying the the post-restoration data would increase the restore time significantly. Can you tell us roughly by how much?

    Thanks,

    Robert
     
  17. lucas1985

    lucas1985 Retired Moderator

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    DVDisaster is da bomb. I can back up system images or plain data to DVD without worries and total confidence.

    On topic: I do both verification (if the app allows this option) and restoring (first to an empty drive and then to the drive being used) for disk images. If all goes well, I store the checksums of the image in a text file (see pics below) and I'm done. This way, I can defrag/move/copy the images files with total confidence.

    screen.png
    check.png
     
  18. RobertB

    RobertB Registered Member

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    How does having the checksums benefit you -- i.e., in what software do you enter them?

    Robert
     
  19. lucas1985

    lucas1985 Retired Moderator

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    In that example I've used HashTab. Storing checksums is an almost bullet-proof way to asses the health of a given file. If you change just a single bit (due to hardware malfunction, software bugs, copy/move errors and so on), the checksums will change and you'll know that those files can't be trusted to restore a perfect copy of your system.
     
  20. Long View

    Long View Registered Member

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    Lucas1985 - not being argumentative - I really would like to know. How often do you find checksums that have changed when you image ? or when was the last time ? My assumption, and I may well be wrong, is that if using a decent imaging program and functioning hardware that a changed checksum ought to be a very rare event ?
     
  21. lucas1985

    lucas1985 Retired Moderator

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    I never had a changed checksum (knock on wood) :) But, since it's a fast, reliable and easy-to-use safety belt, why not?
    - Changed cheksum: I delete the image file (never happened).
    - Matched checksum: If the restore fails (never happened), it is not the fault of the image file.
     
  22. MrBrian

    MrBrian Registered Member

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    Here is an example of why IMHO a verify should be run at least occasionally, even if you never had a previous verify failure. (By the way, a successful restore also qualifies as a successful verify):

    Even if your system has had a perfect record when it comes to backup verification, this is no guarantee that you won't run into backup issues that are non-sporadic in nature in the future.
     
    Last edited: Jun 2, 2008
  23. markymoo

    markymoo Registered Member

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    You right, but you know what? as Windows gets more stable, images are being kept for longer time before being used to restore. In that time the images or the backup media can suffer for lots of reasons too numerous to list. Having a checksum assurance that the images are exactly the same as when you took them is good thing. It is a rare event but it could be 1 in 10 chance of images going wrong. Any extra check is a benefit and anybody keeping important data they can't afford to lose, it is a plus. On a site of security concious i thought this be welcomed not seen as overkill.
     
  24. Long View

    Long View Registered Member

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    Thanks - I have never used checksums. I agree, if fast then why not. will investigate how to use them with images.
     
  25. Long View

    Long View Registered Member

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    Not seen as overkill by me. I just like to be clear regarding cost and benefits.
    Although I stopped using DVD and CD for data storage a few years I do have CD from 1996 which can still restore and DVDs from 2003/2004 the same. My main security on data is to have multiple back ups in multiple locations and multiple media or even different drive manufactures. Over time storage changes. floppie, Zip, jazz, CD, DVD....... and data gets migrated. I could plug in an old jazz drive and probably restore but as all that data is now on external drives why bother. Soon the data will be on solid state drives and all the old sata 2s will go to the tip.
     
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