at boot 

Unlocking rootfs_data ...
switching to jffs2
empty_blocks 0, bad_blocks 0, c->nr_blocks 87
mount: mounting /dev/mtdblock2 on /jffs failed
jffs2 not ready yet; using ramdisk


root@OpenWrt:/# mount
rootfs on / type rootfs (rw)
/dev/root on /rom type squashfs (ro)
none on /proc type proc (rw)
none on /sys type sysfs (rw)
none on /tmp type tmpfs (rw,nosuid,nodev)
tmpfs on /dev type tmpfs (rw)
none on /dev/pts type devpts (rw)
/tmp/root on / type mini_fo (rw)
root@OpenWrt:/# mount -t jffs2 /dev/mtdblock2 /jffs


doing it manually

root@OpenWrt:/# mount -t jffs2 /dev/mtdblock2 /mnt/
mount: mounting /dev/mtdblock2 on /mnt/ failed
Cowardly refusing to erase blocks on filesystem with no valid JFFS2 nodes
empty_blocks 0, bad_blocks 0, c->nr_blocks 87
: mount: mounting /dev/mtdblock2 on /rom/jffs failed