Cyclic Redundancy Check is a common technique for detecting data transmission errors.
As long as you got your data backed up, you have nothing to worry about.
TimeMachine on one powered external drive conected all the time and a Carbon Copy Clone on another disconnected and updated once a week is prefered.
Format both external drives HFS+Journaled in Disk Utility.
Your covered both from human errors and hardware failures as you can hold option key and boot off the clone. 🙂
If your having problems you can try cleaning everything out of your caches and letting the computer rebuild itself.
Downlaod and run ALL the cleaning and maintainece aspects of the FREE OnyX and reboot
http://www.titanium.free.fr/
Hold c and boot off the disk that comes with your comptuer and under the Utilities menu is Disk Utility
Select your drive on the left and Repair Permisisons (ignore what you see)
Then Repair Disk, if you get any errors here that are NOT repaired, then you got a issue with your drive.