How are RST RAID 1 "Verification Errors" detected and repaired?

I'm using RST 12.8.0.1016 on a RAID 1 and I'm seeing "verification errors" when I run the manage->advanced->verify option (never media errors).  The "Cache mode" is set read only, and "Write-cache buffer flushing" is enabled.  This IS NOT a recent issue, I've seen it in older releases of RST.  How are these errors detected, and more importantly, how are they repaired?  AFAIK, with RAID 1, there are only two drives, so when an inconsistency is detected between the drives, how is it decided which drive is valid?  Why are these errors present?  Is there any way to prevent them?  Can I identify where these errors are occurring (what file/location in the array)?

Thanks,

Richard