How to boot new kernel

[Коньков Евгений]

Hi Freebsd-questions.

In system two disks now:

# kenv | grep dev
currdev="disk1s1a:"
loaddev="disk1s1a:"
loader_conf_files="/boot/device.hints /boot/loader.conf /boot/loader.conf.local"
vfs.root.mountfrom="ufs:/dev/ad8s1a"
kern.devalias.ada0="ad4"
kern.devalias.ada1="ad8"

one was with installed FreeBSD (ad4) and second is empty (ad8)
I install new system to ad8 and add to (ad4) /boot/loader.conf next line:
vfs.root.mountfrom="ufs:/dev/ad8s1a"

so next time I booted from second hdd.

But now I have problem.
How to boot kernel from second device instead of first one.

BIOS starts to run loader from first device (ad4) and kernel is booted
from it but all other is mounted from (ad8)

# df -h
Filesystem     Size    Used   Avail Capacity  Mounted on
/dev/ad8s1a      1G    117M    809M    13%    /
devfs          1.0k    1.0k      0B   100%    /dev
/dev/ad8s1e      1G    267M    660M    29%    /tmp
/dev/ad8s1f     39G     23G     13G    64%    /usr
/dev/ad8s1d    5.8G    3.9G    1.5G    72%    /var
procfs         4.0k    4.0k      0B   100%    /proc
devfs          1.0k    1.0k      0B   100%    /var/named/dev

so in memory I have old kenel
uname -a shows that #0: Sat Nov 12 20:17:02 EET 2011
(I have compiled new kenel on 2011 12 03 )
but on disk all is new: kernel and world.
How to force to load kernel from second drive (without access to
machine directly)?