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File Verification

File Verification is the process of verifying that a file has not been changed and/or that two files are identical, bit by bit. ViceVersa supports both types of file verification.

You can verify that files in a specified location have not changed by creating a snapshot of one or more folders at a given time and then re-comparing the folder content with the original snapshot at later time.

You can also verify that two locations have exactly the same files, bit by bit: ViceVersa will calculate the CRC of each file to make sure they are indeed identical. A very important and common task for people working with CD creation is the verification that the data mastered is the same as the original data. For this purpose ViceVersa offers a Cyclical Redundancy Check. With ViceVersa you can determine if even one byte of data differs.

Starting with ViceVersa PRO 3, SHA-256 hash file verification can be used alongside CRC. 

User Comments
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Brian -  02-Apr-08
Hi - when duplicating the contents of one full 120GB drive on to another empty 120GB with both the CRC file verification options ticked I notice that the drive controller statistics state that the source drive has read out 240GB of data with 0 written but the target drive shows 120GB written and ZERO read. Are you sure Vice Versa does file verification properly? From the statistics it looks like it's verifying source against source! (brian_vv AT brianoloughlin DOT com)
TGRMN Software -  02-Apr-08
Hi, as a test, try to manually calculate the CRC of some files on target: in the comparison window select some target files and right click, then From the menu select "calculate CRC". thanks
ArtKns -  22-Sep-12
I don't want to be too pedantic but I respectfully disagree that CRCs ensure identicality. Identical CRC values do NOT guarantee that files are identical - theoretical or otherwise. It only indicates that the files are HIGHLY LIKELY to be identical. (Unfortunately I don't remember enough of group theory to prove it.) Although the possibility exists for false CRC results it is quite small. In my over 30 years of using CRCs I have never known it to fail.

However, this begs the question of how VV files are verified. Is it via CRCs or an actual "bit by bit" comparison? There is a difference.

Since safety is of prime concern in deleting or overwriting "duplicates" my first question was how are files compared. This most important question is not highlighted on the main pages but seems to be buried here. It needs to be fully described and not just dismissed with "according to the current comparison method". What are the methods?
TGRMN Software -  24-Sep-12
The safest method is to use the "both" comparison method in ViceVersa: this method will consider files as being the same only if they have the same name, they are in the same subfolder, they have the same modified timestamp and have the same CRC value. In most applications CRC comparison is not needed, as it takes quite some time to perform.
Kerry -  18-Jun-15
For clarification, when VV creates a "snapshot" of a folder, does that include the CRC information of the original files?
TGRMN Software -  19-Jun-15
It can optionally do both: with or without CRC information included.
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Author: TGRMN Software

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