how to remove HD from LVM on /

[michael]

Hi, I've just received a PC with 2 HDs with LVM. I wish to remove one  
of the HDs (/dev/sdb or /dev/sda???) from the LVM (well I wish to  
install MS WinXP somehow!). However, if I try to remove the HD it  
says (rightly) that it is still in use, but then again I can't  
umount / can I?! I'm also unclear if I need to reduce the filesystems  
somehow.

Here's some more details of what I tried (handtyped since other  
machine isn't on the network). I've Googled about but to no avail.  
Thanks, M



$ mount
/dev/mapper/VolGroup00-LogVol00 on / type ext3 (rw)
...

# vgscan
..
Found volume group "VolGroup00" using metadata type lvm2


# pvdisplay /dev/sda2
--- Physical volume ---
PV Name            /dev/sda2
VG Name           VolGroup00
PV Size               465.66Gb/not usable 3.56MB
Allocatable         yes
PE Size (KByte) 32768
Total PE              14901
Free PE               2
Allocated PE      14899

# pvdisplay /dev/sdb1
--- Physical volume ---
PV Name            /dev/sdb1
VG Name           VolGroup00
PV Size               698.64Gb/not usable 10.34MB
Allocatable         yes (but full)
PE Size (KByte) 32768
Total PE              22356
Free PE               0
Allocated PE      22356

# umount /dev/mapper/VolGroup00-LogVol00
umount: /: device is busy
umount: /: device is busy

# vgreduce /dev/mapper/VolGroup00 /dev/sda2
  Physical volume "/dev/sda2" still in use

# vgreduce /dev/mapper/VolGroup00 /dev/sdb1
  Physical volume "/dev/sdb1" still in use