HP SmartArray P420 Ready for Rebuild

Hello,

I have P420 with 6x WD Red 4Tb in RAID-5. Something happens with it (I can't imagine what's may be wrong - there wan no any failures like as power failure, etc...). Now the logical drive have the status :

Status: Ready for Rebuild
Parity Initialization Status: Initialization Completed

All of physical drives iis in OK state (via hpssacli command). 

After cold reboot server can access to all files on LUN. But status not changed.

I read this forum and found that it may be Unrecoverable Read Error (URE) ssituation. But how to know which HDD failed (or failing) if all of HDD is in OK state?

Thanks,

Anatoly.