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Cyclic Redundancy Check: what is it, and how do I get rid of it on my newly burnt CDs and DVDs?

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Summary: Cyclic Redundancy Check is an error detection mechanism to make sure that your data has been read properly. If a Cyclic Redundancy Check fails, it could mean several things.

When I burn a CD or DVD, I frequently get a "Cyclic Redundancy Check" error when I go to read it. The media has no scratches or anything obviously wrong, so why is this happening? And more importantly, what do I do?

A "Cyclic Redundancy Check", or more commonly just "CRC", is a error detection mechanism that makes sure that the data you're trying to read from media such as hard disks, CDs and DVDs is actually correct. By "correct" we mean that the data you read is in fact the data that was written.

When a CRC check fails, there are several possibilities and places to look.

A CRC works by taking a block of the data that is about to be written to the media, calculating a checksum (basically some math involving all the data, that results in a number), and writing that number, along with the original data, to the media. When the data is later read, that same calculation happens, and if a different number results, then an error is declared - the data read was not the same as the data written.

CRC checks happen each time you read the media. Many CD and DVD burning programs will include a read pass immediately after writing, to ensure that the data was written properly.

There are several ways that a checksum error could happen:

  • A Bad Write: if the device that wrote the media had a problem while writing, it could have written the wrong data.

  • Dirt in the Writer: dust or other obstructions in a CD or DVD writer can interfere with laster and cause the bad data to be written.

  • Bad Media: poor quality media, particularly CDs and DVDs, can sometimes "not take" the data that's written to them. Perhaps there's a flaw in the physical media. These types of flaws may not be visible to the naked eye - even a one-bit error can cause a CRC calculation to fail.

  • Bad Write Alignment: It's fairly obvious that on CDs and DVDs data is written in a circle on the media. However exactly where that circle lands is dependant on the alignment of the drive. It could be slightly off-center, or skewed in some way. This is frequently the case if a CD or DVD reads perfectly on the drive that wrote it, but fails when read on other drives.

  • Scratches and Other Damage: you've mentioned that your media's not scratched, so this may not apply to you, but CRC checking is most commonly thought of as a way to detect errors that result from physical damage to the media after it's been written. And once again remember that a tiny scratch, if in the wrong place, can do damage. If your problem is with multiple CDs or DVDs and you've been handling them properly, then it's unlikely that this is the case.

  • Dirt in the Reader: much like dirt in the writer, dust and other particles can interfere with a CD or DVD reader's ability to read the media properly.

  • Bad Read Alignment: again, much like bad write alignment, if the reader isn't tracking to the same "circle", it may not be able to read the data. Some drives are better at compensating for this than others.

  • Bad Reading Drive: finally, it's always possible that the CD or DVD drive itself is having a problem reading in general.

"If you have a CD or DVD that is reporting a CRC error try reading it on different drives."

As you can see, there are lots of possibilities.

If the problem "travels" with the CD or DVD you've written ... meaning that it fails when read in several different devices, then the problem is most likely with the writer or the media itself.

If the problem happens only when read on one specific reader, then that reader, and not the writer or media, is most suspect.

Make sure that you're using high quality, brand name blank CDs and DVDs. Occasionally clean the inside of your computer, including carefully vacuuming the CD or DVD tray from the outside to remove excess dust. If there is an alignment problem, there's little you can do yourself - you'll need to use another drive.

Can bad data be "fixed"? - in a nutshell, no. I've actually oversimplified the role of a CRC above. It typically includes both error detection and correction. That means that the calculated checksum can often also be used to determine what data is wrong, and return the correct data instead, on the fly. This probably happens often, and you'd never notice. By the time a CRC error has been declared enough errors have occurred that the error correction has failed. At that point, you're pretty much out of luck.

If you have a CD or DVD that is reporting a CRC error try reading it on different drives. As I mentioned above, the ability of drives to compensate for things like alignment problems, or "weak" writes varies, and what's unreadable on one might be readable on another. If you do find a drive that works, copy the data off immediately, and plan on burning it to a new CD or DVD on a writer that's known to be good.

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Recent Comments

The only answer I know of for the CRC error, is to download and use CDCheck on the CD or DVD. It reads and re-writes the whole CD/DVD, to a new folder, until it gets to the problem area. Then, it reads it, sector by sector, and stamps a "0" in an unreadable sector, until it finishes reading the "BAD" part of the CD/DVD and repairing it that way. This works for scratches and other errors on the CD/DVD that causes a CRC. (I think it works for computer files, etc. but I've never needed to try this.) Another trick is to copy all the files with Windows Explorer/My Computer, and only run CDCheck on the file(s) that produces the CRC. Then, from the folder that the repaired and copied files are in...burn that like it was a CD/DVD...this is just faster, CDCheck will do it all for you, it just takes a little longer on files that don't need repairing. Using AnyDVD, in the background, allows one to do this to any copy protected CD/DVD, as well. It works GREAT!!! Good luck and enjoy repairing your messed up CD/DVDs. :-)

Posted by: Ron at October 22, 2007 03:27 PM

i have just finished backing up over 200gb of my files onto dvds only to find that i have been burning CRC errors into many of the discs, is there any QUICK way to test files readability so i can create a list of whats bad and whats not then get the bad files reburnt now the problem is fixed. ive tried CDCheck & IsoBuster they take forever to read the bad files. i need something that can just knock up a disc review quickly is there such a thing?? or maybe a way of reducing the amount of time windows spends tring to reread the bad info? so i can test the discs myself or am i better off starting from scratch?

Posted by: Steve C at October 23, 2007 09:14 AM

i am getting a data error(data2.cab)(cyclic redundancy check error when iam installing a game.....plzz help me out from this ...how do it get rid of crc erroe

Posted by: srikanth at October 28, 2007 12:22 AM

Dear Leo,
I have tried everything recomended on this site about CRC. But nothing works. My friend said that he would let me borrow a DVD for a week with some files and pictures of his trip to places around the world, and I was so excited because he gave me permission the make a copy so I can keep a copy. But when I tried to copy it, "Error, Cyclic Redundancy Check" pops up everytime. There isn't an scratches on the disk, nothing's wrong with my computer DVD drive reader. I even tried to copy the file on my other desktop and my second laptop, but nothing. Please help:(

Posted by: Kalas at December 4, 2007 02:04 PM

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Some combination of the problems listed in the article may simply make it
impossible for you to read that DVD. Have your friend make sure he can still
read it, and if possible, burn you another copy.

Leo


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Posted by: Leo A. Notenboom at December 5, 2007 09:30 AM

CRC errors can also be caused by IDE cables being too close to each other, or too long.

Posted by: voodoomedicine at December 5, 2007 05:22 PM

Hi all,

SOLUTION: I also had problems with the CRC error when burning games. My try has been with two .rar games. What I did what was just to descompress the total file.rar into my PC and to install the games directly from the given data,through the setup.exe , without burning the game.
When I was installing the game from the DVD I was getting the error but the same file descompress and installed without burning had succesful results. I hope it can help, though I know my comment is not very professional

Posted by: Tuny at December 13, 2007 12:37 PM

Leo, I need your help. I had copied some video files that I had purchased off a website and burned them to a c.d. Now, the c.d. worked fine but about a year later, I'm getting the cyclic redundancy message. I think my first mistake was using memorex c.d.s as I've used the Sony brand and they haven't been giving me any trouble so far.

I've tried everything: copying files to my desktop, to a folder, burning to DVD (I've lost three so far because of the error message) and I've even tried windows media maker on my desktop and laptop to try and save the video files. This isn't the first time this has happened to me and I'm trying to avoid erasing the disc altogether as I spent a lot of money obtaining these video files. Is there any way to save what I have without erasing everything?

Posted by: Paul at January 14, 2008 10:39 PM

I am getting a CRC error on a DVD with .NEF (Nikon RAW) photo files. For at least some of the troubled photos the thumbnail shows up, and Adobe can open a larger version as well so there must be enough data for that at least. Only it won't let me COPY what I DO have. Some of them don't display thumbnails; I assume these are lost causes - there may have been some dust exposure to the burner that wrote the DVD which could have corrupted the totally lost files.

Posted by: Anna at March 3, 2008 11:06 AM

Movies will play with CRCs no problem but they won't write. We need to disable CRCs during the write. Any ideas?

Posted by: Chris B. at August 1, 2008 06:40 AM

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