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A Brilliant File Verification tool: A Second Opinion For Your Data’s Integrity.
All of us copy files from time to time, whether that is just moving some valuable documents to a thumb drive, backing up some folders from one hard drive to another, or using a synchronization program to make duplicates of important data. Many of us have probably also experienced the gut-wrenching feeling when we discover that those copies which we were depending on turn out to be damaged or corrupted in some way and are unusable.
Many file backup and folder synchronization programs perform some sort of file verification on their own. Still from time to time I have seen where even that has failed because of a bug or another glitch. When you simply copy files using Windows Explorer, cycle redundancy checks (CRC) are performed on files to help insure copy integrity, yet occasionally you still end up with corrupt files on the other end.
To avoid such problems, special tools have been developed to do more thorough checks in order to confirm the consistency of files. Most of these tools employ various checksum or hash check methods to examine the contents of each file for discrepancies. Every file has an unique checksum so if the file is changed in the slightest way it will be detected.
This technique has been commonly used to make sure files downloaded from the Internet are complete and unchanged in any way. If you have ever seen a string of numbers called a MD5 or SHA1 sum listed next to a file download that is what those are there for. This same technique can also be used to verify that the files you copy from one location to another are complete and unchanged.
ExactFile. This is the only free checksum utility I have found that includes a feature which makes it truly easy to do hash checks on large sets of files. Its usage is simple. You click the button labeled “Create Test File Applet” which creates a “digest” of the files in whatever folder you wish. It also places a small 360Kb executable file in the same folder. After you move your files you simply double click the TestFiles.exe and it will verify the integrity of those files. Not only will it indicate if a file is incomplete or changed in some way, it will also report if any files are found to be missing.
One possible scenario would be to use it along with a backup program to verify the files in your “My Documents” folder after a backup is completed. First you would run ExactFile and create a TestFile applet. Next perform the actual backup, and finally run the TestFile applet on the backup files. There is a command line version of ExactFile that could be used with backup programs that have the ability to perform pre and post backup job tasks. You would set up your backup program to run the commands to create the digest, before performing the backup, and to verify the files automatically for you afterwards.
One limitation to using ExactFile with backup programs, is that they often store files in special compressed archives. You will only be able to use ExactFile with uncompressed mirror style backups. If your backup program uses Zip compression to archive files, you could possibly use ExactFile in conjunction with a program like WinMount or Pismo File Mount which can mount a Zip file as a virtual drive after which the TestFile applet could be run as normal.
ExactFile is particularly useful for checking the integrity of files backed up to optical media (CD or DVD). It is also quite useful to make sure that files synchronized to another computer or network share have arrived intact.
This is a great little utility with a lot of potential uses. Hopefully you will find it as useful as I have. If you know of any other programs with similar abilities, be sure to let us know in the comments below. Both the gui version and the command line version of Exactfile can be found on the developer's site. Please note that both are still in beta but with my testing, on Win 7, I found them completely stable and bug free.
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For checking that a large folder has been copied (not imaged) exactly I have been using CDCheck. You can have it perform a binary comparison (bit by bit). You can also perform Hash check and check that files are readable. Despite the name 'CDCheck', you can check and or compare files on any media, including hard drives.
It is easy to use and has been around for years. It's described on this website so just put CDCheck in the search box.
Cheers,
I use a file-hashing utility called md5deep, freeware, originally developed by...the NSA. It's command-line only, but once you get used to it, it's fairly easy, and if you needed, you could put your most-used commands in a *.bat file.
I use it for testing CDs full of software installers for deployment across a large network; the first thing I do is output a set of file hashes from my originals thusly:
>md5deep.exe -r C:\my\original\folder\* > installers.md5.txt
This hashes files recursively in the specified folder and its subfolders, and outputs the results to a log file named installers.md5.txt.
Next, I check the CD (the X: drive, into which I have copied my original folder):
>md5deep.exe -x C:\path\to\installers.md5.txt -r X:\*
....This command outputs the names of any files that show up on the CD, but do NOT match a hash from a file in the original folder...in other words, files which may be corrupt, or which have changed since the last backup.
Lastly, I do
>md5deep.exe -x C:\path\to\installers.md5.txt -n -r X:\*
....This goes through the CD recursively, and shows any files that were in the log (and thus, the original folder), but aren't on the CD.
I know, I know, IT'S COMMAND-LINE GOBBLEDEEGOOK! But seriously, it's simple and easy once you get familiar with the commands.
I use a small tool called DVDsig available from http://members.ozemail.com.au/~nulifetv/freezip/freeware/
It was written to allow verification of files burned to DVD, but it works just as well for verification of files anywhere on your hard drive or network. It is simpler to use than the tool you recommend above, and works fine for verification of backups.
I've used it for a couple of years now, and it works great.
Thanks Rob for mentioning this. It is always good to have alternatives. Often times the value such little utilities are overlooked, but when you find yourself needing one, they are invaluable.
Ritho
Editor
Thanks very much for that. I've been after just such a tool (free) for some time as I've too often found that backup software doesn't always copy files faithfully and I'm unaware there's a problem unless I do a laborious manual check for file integrity.
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