URE

The URE rate is the average value that disk manufacturers provide for a disk model (not the individual disk). A value of 10^-14 would mean that an unrecoverable read error will occur during the 12 TB (100,000,000,000,000 bit) process.

Example: A RAID 5 with three 500 GB hard disks, taking into account the URE mentioned above, would mean a statistical failure of a rebuild in 8% of all cases. A URE is much more likely to occur when using higher capacity hard drives.