extrootがうまく行かないのでフォーマットしてみました。

root@OpenWrt:/usr/sbin# mkfs.ext3 /dev/sda2
mke2fs 1.41.11 (14-Mar-2010)
Filesystem label=
OS type: Linux
Block size=1024 (log=0)
Fragment size=1024 (log=0)
Stride=0 blocks, Stripe width=0 blocks
32128 inodes, 128008 blocks
6400 blocks (5.00%) reserved for the super user
First data block=1
Maximum filesystem blocks=67371008
16 block groups
8192 blocks per group, 8192 fragments per group
2008 inodes per group
Superblock backups stored on blocks:
        8193, 24577, 40961, 57345, 73729

Writing inode tables: done
Creating journal (4096 blocks): done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 38 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.
root@OpenWrt:/usr/sbin# tune2fs
-ash: tune2fs: not found
root@OpenWrt:/usr/sbin# ls
brctl             iptables          iwpriv            pppd
chroot            iptables-restore  iwspy             telnetd
crond             iptables-save     mke2fs            uhttpd
dnsmasq           iw                mkfs.ext2         wpa_supplicant
dropbear          iwconfig          mkfs.ext3         wpad
e2fsck            iwgetid           mkfs.ext4
hostapd           iwlist            ntpd
root@OpenWrt:/usr/sbin#

フォーマットしなおしてもダメです。
root@OpenWrt:~# opkg remove block-hotplug
Removing package block-hotplug from root...
root@OpenWrt:~# ls
root@OpenWrt:~#
hotplugを外してみました。

かわりませんねぇ
root@OpenWrt:/mnt/sda2# cd ..
root@OpenWrt:/mnt# opkg remove block-extroot
Removing package block-extroot from root...
root@OpenWrt:/mnt# opkg remove block-mount
Removing package block-mount from root...
Not deleting modified conffile /etc/config/fstab.
root@OpenWrt:/mnt# opkg install block-mount
Unknown package 'block-mount'.
Collected errors:
 * opkg_install_cmd: Cannot install package block-mount.
root@OpenWrt:/mnt# cd /
root@OpenWrt:/# cd etc
root@OpenWrt:/etc# cd config
root@OpenWrt:/etc/config# ls
dhcp      firewall  luci      system    uhttpd
dropbear  fstab     network   ucitrack  wireless
root@OpenWrt:/etc/config# cat fstab

config 'global' 'automount'
        option 'from_fstab' '1'
        option 'anon_mount' '1'

config 'global' 'autoswap'
        option 'from_fstab' '1'
        option 'anon_swap' '0'

config 'swap'
        option 'device' '/dev/sda1'
        option 'enabled' '0'

config 'mount'
        option 'device' '/dev/sda2'
        option 'fstype' 'ext3'
        option 'target' '/mnt/sda2'
        option 'enabled' '1'

config 'mount'
        option 'device' '/dev/sda3'
        option 'fstype' 'ext3'
        option 'target' '/mnt/sda3'
        option 'enabled' '1'

root@OpenWrt:/etc/config# opkg update
Downloading http://downloads.openwrt.org/backfire/10.03.1-rc6/ar71xx/packages/Packages.gz.
Inflating http://downloads.openwrt.org/backfire/10.03.1-rc6/ar71xx/packages/Packages.gz.
Updated list of available packages in /var/opkg-lists/packages.
root@OpenWrt:/etc/config# opkg install block-mount
Installing block-mount (0.1.0-2.1) to root...
Downloading http://downloads.openwrt.org/backfire/10.03.1-rc6/ar71xx/packages/block-mount_0.1.0-2.1_ar71xx.ipk.
Configuring block-mount.
Collected errors:
 * resolve_conffiles: Existing conffile /etc/config/fstab is different from the conffile in the new package. The new conffile will be placed at /etc/config/fstab-opkg.
root@OpenWrt:/etc/config# ls
dhcp        firewall    fstab-opkg  network     ucitrack    wireless
dropbear    fstab       luci        system      uhttpd
root@OpenWrt:/etc/config# cat fstab-opkg
config global automount
        option from_fstab 1
        option anon_mount 1

config global autoswap
        option from_fstab 1
        option anon_swap 0

config mount
        option target   /home
        option device   /dev/sda1
        option fstype   ext3
        option options  rw,sync
        option enabled  0
        option enabled_fsck 0

config swap
        option device   /dev/sda2
        option enabled  0

root@OpenWrt:/etc/config# opkg install block-extroot
Installing block-extroot (0.0.1-2.1) to root...
Downloading http://downloads.openwrt.org/backfire/10.03.1-rc6/ar71xx/packages/block-extroot_0.0.1-2.1_ar71xx.ipk.
Configuring block-extroot.

/etc/fstab -> /tmp/fstab
となっていてリンク切れが発生している。
Init.dのfstabがdisableになっているので、これをenableに切り替えてみた。
そして再度extrootを…
変わりませんでした。