shinju

Not sure if you sorted it but i had the same issue. 2tb WD green drive red balled and i purchased a 4tb WD Red drive to replace. After a 35 hour pre-clear, i stopped the array, replaced it with the new pre-cleared 4tb drive and began the rebuild. Immediately, i noticed it came up as "un-mountable drive detected" but i thought it may clear after the rebuild completed but Alas, 20 hours later with data rebuilt, i could not mount it. I used the format all unmountable drives option and that cleared it right up. Its now mounted with parity check running.