One thing:must copy some data to the pool,remove one disk,shutdown,add a new disk,start the box,get the panic. My box uname -a: FreeBSD freebsd.lpcy.com 7.1-PRERELEASE FreeBSD 7.1-PRERELEASE #0: Tue Oct 21 12:02:30 CST 2008 lhm at freebsd.lpcy.com:/usr/obj/usr/src/sys/lhmwzy amd64