CentOS - Oct 2008 - resize LVM (ext3)

Hello guys,

my scenario is following


   1. I have LVM group named "system"
   2. I have a logical volumes
      - system/root , ext3 mounted as / (20GB)
      - system/swap, swap
      - system/home, ext3 mounted as /home (431GB)

I need to shrink system/home to 80GB (currently there is 57GB used) and use
free space to create another logical volumes.

My scenario is


   1. reduce ext3 fs size to 80GB by using resize2s
   2. reduce system/home size by using lvreduce
   3. create another logical volumes

Questions


   1. How can i be sure that i will shrink ext3 to exact size 80GB and that
   the same will lvreduce do? I do not want to cut from ext3 filesystem if i
   will reduce logical volume too much
   2. Can you please send me commands to achieve 1) and 2) part of my
   scenario?
   3. Or can i just use lvreduce and my ext3 will shrink automatically?
   4. Do i need to umount system/home when resizing?

Thanks in advance!

David
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On Wed, Oct 29, 2008 at 12:58:32PM +0100, David Hl??ik wrote:
<snip>
>    1. How can i be sure that i will shrink ext3 to exact size 80GB and that
dev=/dev/system/home
resize2fs $dev 80G

Then, to be sure of the real size:
blks=$(tune2fs -l $dev | awk -F: '/Block size/ { print $2/512 }')
fssize=$(tune2fs -l $dev |
  awk -v bs=$blks -F: '/Block count/{print $2*bs}')

Now, $fssize has the complete size in bytes. Verify it:
echo $fssize

Now, for lvresize:
lvresize -L 80G system/home

Verify that the printed target size matches the wanted value.
>    3. Or can i just use lvreduce and my ext3 will shrink automatically?
NO! lvreduce doesn't care about what's inside, and will happily lose
data.
>    4. Do i need to umount system/home when resizing?
Yes, and you must do a full fsck also:

e2fsck -f /dev/system/home

Regards,
Luciano Rocha

-- 
lfr
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>
>
> Now, for lvresize:
> lvresize -L 80G system/home
Are you sure there should not be lvreduce -L 80G system/home ?

Thanks!

D.

Hi,

On Wed, Oct 29, 2008 at 07:58, David Hl??ik <david at hlacik.eu>
wrote:
> How can i be sure that i will shrink ext3 to exact size 80GB and that the
> same will lvreduce do? I do not want to cut from ext3 filesystem if i will
> reduce logical volume too much
Reduce the filesystem to 78G or 79G with resize2fs, then reduce the LV
to 80G, then grow the ext3 filesystem again to fill all the LV. This
should make it safer when cutting the LV.

HTH,
Filipe