1. create physical volumes
pvcreate /dev/xxx
2. create volume groups from physical volumes
vgcreate vg0 /dev/xxx
3. create logical volumes from volume groups
lvcreate -L3800G vg0
unfornutantely you couldn’t make logical volume what is use all free space automatically. you need exactly specify the size of logical volume. if you want know the available free space you can see with vgdisplay.
Free = PE Size * Free PE