WHEN IS A COPY NOT A COPY?
Q As I’ve been working up in my skill level, I seem to be trusted more with the day’s files for a shoot. There seem to be certain ways that people think are best for dealing with all of the data. I think I’m pretty good with making multiple copies of each file and making sure those copies are on separate high-quality drives. I also make sure that the folder structure is correct and consistent, and that the drives end up at the right place. My only gray area is the type of copying. Does it really matter if you just do a regular copy or use some sort of software to make the copy? A copy is a copy, right?
A That’s a big gray area, but I can understand your confusion: Digital is digital, right? It’s either copied or it isn’t.
That final step from camera card to media drive is critical. If it has to work nine times out of 10 or 99 times out of 100 (or some other ratio), using the operating system to make the copies works fine. However, it’s that one time when the file shows up as "unreadable" that makes you worry.
The operating system’s method of copying files basically checks to make sure there were no errors during the file copy process and ensures that the operation completed. Usually that’s enough. But if you’re taxing the operating system by copying to multiple drives or accessing other files to check playback, errors can go unnoticed.
A better way to copy files is to verify the file once it has been copied. There are third-party applications (a popular one is ShotPut Pro), as well as components in larger cloud suites like Adobe Prelude that offer file verification during the transfer. The verification level provided corresponds to the accuracy and speed of the copying. Most applications offer a basic file size check. Once the data is copied, the software compares the number of bits in the copy to the size of the original. This is a fast and efficient process.
If you want greater peace of mind, use an advanced verification like a checksum algorithm. A checksum method looks at the actual data in the file and creates a fingerprint that represents that data. Once the file is copied, the data in the copy is used to create another fingerprint. Faster than you can say CSI: Las Vegas, the two fingerprints are compared and the software confirms whether the files are identical. There are various types of checksum verifications. Two that are frequently available are MD5 and CRC. MD5 seems to be the method of choice.
Bit-for-bit comparison is another option that actually compares each piece of copied data with the original. Unfortunately, it takes a great deal of time to complete the verification.
The more thorough the verification, the longer the copying process takes. If you have a limited amount of camera cards, you might need to process them more quickly and thus not be able to use the most thorough method.