When you copy a file, there is no guarantee that your file will actually copy 100% error free.
This is why CRC (cyclic redundancy check) checksum file data error checking exists but few people make use of this function due to a lack of knowledge.
Any important data should have its CRC value calculated using one of the many algorithm methods, typically MD5 or SHA1 or SHA256.
In simple terms, a bit of software will total up all the values inside of a file and produce a simple short text value which can then be used at a later date to validate the file is still exactly the same as it was before.
The best method of using this long term is to have the software store these checksum CRC values in a text file located in the same folder as the files you are wanting to keep safe or at the root of the drive as a master checksum directory.
It is best to do these checks during large or important file transfers from device to device and then periodically on any data that is stored long term on any type of media – internal/external HDD/SSD drives including RAID NAS systems, USB sticks, DVD/MDISC and even including cloud.
Here are two easy methods to use CRC data error checking when file copying:
1: Use software like Syncback Pro that will allow you to choose Integrity Checking on the source and destination. When setting up a copy profile, in settings enable the Copy/Delete tab that allows you to tick the ‘Verify that files are copied correctly’ box. You may find other software that works but we do trust Syncback and have been using it extensively for many years.
2: Alternatively prior to copying any files, generate a CRC checksum file that includes all files in each folder.
We recommend EF CheckSum Manager – There is free fully working demo available and if you need to purchase it, then its about $15. In this software: – highlight a folder – choose ‘Create CRC Checksum’ – Create: ‘One checksum file per folder’ – Select SHA256 as Checksum file type – Tick ‘Recuse folders’ – Tick ‘Overwrite existing checksum files’ – Tick ‘Add * to checksum files – Tick ‘UNIX format’ – Tick ‘Verify after creating. Then let it run until it has created these CRC files for each folder which you will see as .sha files in plain text per folder.
You can even then double check by verifying again by highlighting the folder again and choosing ‘Verify CRC Checksums’. If there errors at this point then you have a different problem. The software will give a long list of what passed and what failed.
Now you are ready to migrate all your files and when the files have finished copying to new storage location, run the EF CheckSum Manager again and choose the new location but this time critically choose to ‘Verify CRC Checksums’ – don’t accidently create the checksums again otherwise this will be all for nothing.
Other software we attempted to use that didn’t quite make the grade but worth mentioning was:
ExactFile, TeraCopy, SFV Checker, MultiHasher, RapidCRC, File Checksum Utility, WinMerge, Multi Commander.
ExactFile was really good but its no longer in development.
Here is a video demonstrating file corruption: