Data integrity question- how much verification by SuperDuper?

[stevea]

Originally Posted by dnanian

We don't do any kind of "explicit" verification, since the disk controller itself performs that task for us.

Our general take is that you don't ask the Finder to verify things when you copy, and you don't do it when you write a file to disk with an editor (or whatever). That's because a hard disk has "built-in verification" -- its controller flags errors when they occur, on either read or write.

If we hit an error like this, we stop, because there's been a problem. But compare-after-write would both take time and cause unnecessary wear and tear on the drive.

(This is different from writing to a medium that is inherently prone to failure, like "older" Travan tapes, CDs or floppies...)

Yes, the built-in verification prevents media errors or device errors... but, it does not prevent errors or verify that the files are copied correctly to begin with. (For example, are all files copied? are permissions correct? etc.)

Also, the SuperDuper documentation specifies that "[files which Apple recommends not to copy]" are not copied... yet, there is no explicit documentation or verification to determine exactly what is copied and what is not copied.

Thus, it is not possible to determine if the backup copy is identical to the original or not. Presumably, it is not identical... but, not knowing the exact differences, makes it more difficult to determine if data integrity was maintained or not.
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