[CentOS] Resizing est4 filesystem while mounted

[Dennis Jacobfeuerborn]

On 06/15/2012 09:10 PM, Jeff Boyce wrote:
> Greetings -
> 
> I had a logical volume that was running out of space on a virtual machine. 
> I successfully expanded the LV using lvextend, and lvdisplay shows that it 
> has been expanded.  Then I went to expand the filesystem to fill the new 
> space (# resize2fs -p /dev/vde1) and I get the results that the filesystem 
> is already xx blocks long, nothing to do.  If I do a # df -h, I can see that 
> the filesystem has not been extended.  I could kick the users off the VM, 
> reboot the VM using a GParted live CD and extend the filesystem that way, 
> but I thought that it was possible to do this live and mounted?  The RH docs 
> say this is possible; the man page for resize2fs also says it is possible 
> with ext4.  What am I missing here?  This is a Centos 6.2 VM with an ext4 
> filesystem.  The logical volumes are setup on the host system which is also 
> a Centos 6.2 system.

You didn't really specify your topology accurately so I assume you used
lvextend on the host side. This will not be visible until you rebooted the
guest.

The only way to resize without taking the system offline is to use lvm in
the guest. Add a new virtual disk on the host side which results in a
hot-plug event in the guest (i.e. you should see the new drive added in the
guest). Now create a single partition on the drive (this is important!) and
use pvcreate to turn it into a physical volume. Now add the new PV to the
Volume Group. Finally you can lvextend the LV in the guest and resize the
filesystem.

The partitioning of the new disk in the guest is important because if you
use the disk directly as a PV then this PV will also be shown on the host.
An alternative is to modify the LVM filters in /etc/lvm/lvm.conf on the
host to specifically not scan the LV for the new disk.
I find it easier to create a partition though (i.e. use /dev/vda1 instead
of /dev/vda as the PV).

Regards,
  Dennis