Linux Logical Volume Manager LVM

Logical Volume it contain the following things, logical block device, physical volume, Volume group, and the final one is logical volume. Group of the Linux block device with pvcreate command it create physical volumes then using vgcreate it create column group and finally with lvcreate command it will create Logical volumes.
LVM create a higher lever layer of abstracting than traditional linux disks and partitions.This allows flexibility in allocation for storage. LVM managed volume can also have sensible names like database or home rather than the “sda” and “hda” device names. 
IDE Drive Represent as hda ,
SCSI  Drive Represent as Sda
Pen drive Rep resend as sdb
Lvm Reduce Extended
http://studentwebsite.blogspot.com/2010/05/lvm-extend-reduce-lvextend-lvreduce.html