about df and lvm

[tq01azk]

test environment:
centos 4.4 
Linux localhost.localdomain 2.6.9-55.0.12.ELsmp #1 SMP Fri Nov 2 11:19:08 EDT 
2007 i686 i686 i386 GNU/Linux
lvm> version
  LVM version:     2.02.21-RHEL4 (2007-03-26)
  Library version: 1.02.17-RHEL4 (2007-04-24)
  Driver version:  4.5.5

I creat  4G of size  lvm  partition.

#df -h 
/dev/mapper/lvtest-lv    4.0G  2.6G  1.3G  68% /mnt/lv
#lvdisplay
 --- Logical volume ---
  LV Name                /dev/lvtest/lv
  VG Name                lvtest
  LV UUID                t4tXV0-UE5j-K7oq-IoXj-hXfP-mgej-CWXQVA
  LV Write Access        read/write
  LV Status              available
  # open                 1
  LV Size                4.09 GB
  Current LE             131
  Segments               1
  Allocation             inherit
  Read ahead sectors     0
  Block device           253:2

then I use the command "lvextend" to add 800M capatity into the lvm.
but i also see the capatity is 4G by using df,lvdisplay show right information

#lvextend -L +800M /dev/lvtest/lv  
Extending logical volume lv to 4.88 GB
Logical volume lv successfully resized
#df -h
/dev/mapper/lvtest-lv    4.0G  2.6G  1.3G  68% /mnt/lv
#lvdisplay 
  --- Logical volume ---
  LV Name                /dev/lvtest/lv
  VG Name                lvtest
  LV UUID                t4tXV0-UE5j-K7oq-IoXj-hXfP-mgej-CWXQVA
  LV Write Access        read/write
  LV Status              available
  # open                 1
  LV Size                4.88 GB
  Current LE             156
  Segments               1
  Allocation             inherit
  Read ahead sectors     0
  Block device           253:2









2007-12-04 



tq01azk