Most of time on system we see ATA disk timeout, we need to check the cable first. But what if there’s no cable, and smartmontools shows no significant fault? Here is my tip that works on FreeBSD: turn of apm feature of the disk. Put this line in the /etc/rc.local
/usr/local/sbin/smartctl -s apm,off /dev/ada0
Reference: somewhere on FreeNAS fornum.