A read error was encountered during a rebuild and the controller is configured to ‘ignore ECC’ or to ‘Force continue on source errors’. The sector in error was reallocated.This will cause uncorrectable blocks to be rewritten, but the data may be incorrect.
For Mac OS X, you can use the First Aid tab in the Disk Utility—select the disk on the left and then click Verify Disk. If verification encounters problems, you can then use the Repair Disk option on the same screen.