Conceptually for the creation of the mirror to succeed all data from the source volume must be readable so that the destination disk contains an exact copy of the source.
All modern SATA drives have internal machinary to automatically remap bad blocks to an alternate location. Drives can do this remapping automatically under certain conditions such as on a write failure to a certain location. Drives cannot however remap on a subsequent read failure as the contents of the disk can't be read to remap the data. Thus leaving the error be is the least destructive behavior possible for the disk drive.
With todays massive multi-TB drives this happens even to an otherwise perfectly health disk. Just because a few blocks are not readable does not automatically follow by itself the disk is bad or needs to be replaced.
chkdsk commands to detect and repair bad blocks are meaningless when you setup a mirror in windows and most other operating systems. Chkdsk will not correct these problems. The reason is chkdsk works at the file system level and stores bad blocks in the filesystems structure. RAID works at the disk level below the file system and thus is totally oblivious to both the existance of NTFS and NTFS's bad block list.
The way to fix read errors on disks with internal remapping is simply to write to blocks that can't be read. If the area is defective the disk will remap the area transparently and subsquent reads to it will then succeed. This is quickest and least effort path to correcting a read error so the disk can be synced up but perhaps not the safest as the act of writing seals all hope of recovering the unreadable data. Also if applicable writing to a disk you may otherwise suspect to be faulty is not a winning policy.
Unfortunatly I do not know of the existance of a utility that will read and overwrite bad blocks if they cannot be read after a reasonable number of read attempts have exhasted. Previously I've had to use 'dd' to do this manually by scanning for unreadable locations and writing over them.
A much safer way is to make a copy of the disk using a tool such as ddrescue (Boot with g4l (Ghost4Linux) iso image available from sourceforge) dd rescuse starts by copying as much data as it can then finally retries those blocks with read errors until all retries have been exhausted. If you suspect the drive may be failing this is a much safer approach.