Here's my mount table after a clean start. Notice that my harddisk (/hdd) mount point is mounted twice, and so is /var/mnt/usb and few others.
/dev/root on / type squashfs (ro)
none on /dev type devfs (rw)
/proc on /proc type proc (rw,nodiratime)
devpts on /dev/pts type devpts (rw)
/dev/mtdblock/1 on /var type jffs2 (rw,noatime)
none on /tmp type ramfs (rw)
usbfs on /proc/bus/usb type usbfs (rw)
/dev/ide/host0/bus0/target0/lun0/part1 on /hdd type ext3 (rw)
/dev/scsi/host0/bus0/target0/lun0/disc on /var/mnt/usb type ext3 (rw)
/dev on /dev type devfs (rw)
/proc on /proc type proc (rw,nodiratime)
devpts on /dev/pts type devpts (rw)
usbfs on /proc/bus/usb type usbfs (rw)
/dev/ide/host0/bus0/target0/lun0/part1 on /hdd type ext3 (rw)
/dev/scsi/host0/bus0/target0/lun0/disc on /mnt/usb type ext3 (rw)
none on /tmp type ramfs (rw)
Here's the disk free output:
~ > df
Filesystem 1k-blocks Used Available Use% Mounted on
/dev/root 247791 27908 207090 12% /
/dev/mtdblock/1 247791 27908 207090 12% /var
/dev/ide/host0/bus0/target0/lun0/part1 20006504 52740 19953764 0% /hdd
/dev/scsi/host0/bus0/target0/lun0/disc 247791 27908 207090 12% /var/mnt/usb
/dev/ide/host0/bus0/target0/lun0/part1 20006504 52740 19953764 0% /hdd
/dev/scsi/host0/bus0/target0/lun0/disc 247791 27908 207090 12% /mnt/usb
When I umount my harddrive I still see it as mounted? And the funny thing is, it has the same amount of space as my USB key.
~ > umount /hdd
~ > df
Filesystem 1k-blocks Used Available Use% Mounted on
/dev/root 247791 27908 207090 12% /
/dev/mtdblock/1 247791 27908 207090 12% /var
/dev/ide/host0/bus0/target0/lun0/part1 247791 27908 207090 12% /hdd
/dev/scsi/host0/bus0/target0/lun0/disc 247791 27908 207090 12% /var/mnt/usb
/dev/scsi/host0/bus0/target0/lun0/disc 247791 27908 207090 12% /mnt/usb
I checked /etc/fstab and there's no entry, I examined the /etc/init.d/rcS and it seems that few filesystems get mounted from there.
Could anyone explain it to me like a six year old kid, who's mounting my /hdd and I don't know about ? And why's he doing it ?

Thanks!