Data integrity question- how much verification by SuperDuper?

[marianco]

Steve,
I don't think your example is a good one. If a user deliberately makes changes to a disk while SuperDuper is running a backup, they should automatically realize that the changes may not be copied over the the backup. The solution would be to run SuperDuper again to update the changes. If anything, the user should refrain from using the Mac while running SuperDuper to avoid problems like this.

I also thought Dave's answer was pertinent and sufficient. The disk driver itself does the verification of the copy, otherwise verification becomes impractically time-consuming. SuperDuper's cloned disks have been the best, cleanest, most problem-free I have obtained from any utility so far. This includes Synchronize Pro (which I now use only for synchronization of folders) and Carbon Copy Cloner. What makes it so good is that even the aliases point to the correct files in the clone. Note that Synchronize Pro does have a simple veriication procedure (checking file size, various flags, etc) which is relatively quick. I have used this, but it hasn't been very useful since too many files are listed as different, when the data in the file I know is identical. After a while, I ended up ignore the listing of files the verification process made in Synchronize Pro's log file.

Your initial scenario of copying a drive with known severe directory/corruption problems is also problematic. I don't think you can reliably get a clone of that drive in the first place, since the files themselves cannot be reliably found. By the way, I did have such a drive once - where Disk Utility and Disk Warrior both reported the drive was too damaged to use. In this case, I don't know which helped but I ran Norton Utilities' Disk Doctor (which is why I still keep it around) and did a Safe Boot (holding the shift key while starting up, which runs the fsck command-line utility), and the drive was repaired. If the drive is corrupted beyond the usual repair utilities, you may have to use Data Rescue (a third party utility), to scavenge the drive and attempt to recreate its files and structure on another drive. Data Rescue is probably the best at doing this.

If you really want to verify the exact file differences between the original and the clones, a utility that can do this very well is "You Synchronize". It uses CRC32-bit checksums to determine if files are different before synchronization. This is far more sophisticated than checking file lengths or modification dates. This will definitely tell you what differences there are between the original and clone. The problem is that if you have hundreds of thousands of files (as many people often have these days), it literally takes hours upon hours to complete the verification since You Synchronize has to do the CRC 32-bit checksum for each file on the original and each file on the clone, then compare the checksums then add the data to its database. For myself, this made it very impractical to use on a daily basis - particularly since I like backing up to four clone hard-drives daily. I would be limited to one overnight synchronization a day if I used You Synchronize on anything but a small number of files.
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marianco