[CentOS-virt] Resize guest filesystem question
markus.falb at fasel.at
Mon Feb 27 08:04:56 EST 2012
On 24.2.2012 21:05, Jeff Boyce wrote:
> Greetings -
> I am going through some testing steps to expand a logical volume and the
> corresponding filesystem on a KVM guest and have run across a deficiency in
> my knowledge. I spent the afternoon yesterday googling for answers, but had
> have come up blank still. What I am trying to do is resize the file system
> to use the additional disk space that I added to the logical volume that the
> guest uses. Here is what I have done and the details of my system.
> 0. Both my host and guest are running Centos 6.2.
> 1. My KVM host system has the LVM volume group that is divided into logical
> volumes which are then presented to the KVM guests as raw space.
> 2. A guest may use 2 or 3 logical volumes from the host system for its
> filesystem (/, /var, /data) and I have logical volumes named within the host
> system by guest and mount point so that I know what each logical volume is
> assigned to by it's name.
> 3. I expanded a specific logical volume on the host (/dev/vg/lv_guest1root)
> that is used by Guest1, and I can see in vgdisplay and lvdisplay that the
> logical volume was properly expanded.
> 4. I then issued a resize2fs /dev/vg/lv_guest1root command (on the host)
> to resize the filesystem to the expanded logical volume. This resulted in a
> message that it essentially couldn't find a valid filesystem superblock.
> Well of course then I realized that there is no filesystem on the logical
> volume from the perspective of the host. The filesystem wasn't set on the
> logical volume until the guest installation occurred.
> 5. So then I switched over to the guest system and ran df -h to see the
> existing filesystem
> [root at guest1 jeffb]# df -h
> Filesystem Size Used Avail Use% Mounted on
> /dev/vda2 4.5G 2.3G 2.0G 53% /
> tmpfs 1004M 88K 1004M 1% /dev/shm
> /dev/vda1 485M 30M 430M 7% /boot
> /dev/vdb1 2.0G 219M 1.7G 12% /var
> 6. Then I ran resize2fs /dev/vda2 and got the result that the filesystem
> is already xx blocks long. Nothing to do!
> So here is where I am stuck. Guest1 is my test system so it only has the /
> and /var logical volumes, whereas the production guest (guest2) that I will
> be expanding also has /data, which will be the logical volume that I will
> expand. So two things I did not do where, I did not shut down the guest VM,
> and I did not unmount the filesystem before asking it to resize. However my
> research before doing this did not seem to indicate that I had to do either,
> and the message about nothing to do also seems to indicate that they were
> not necessary.
> So I am missing a hole in my knowledge and additional googling has not
> helped to fill it. I must be missing something simple. Is this result due
> to the fact that I am testing on expanding the / filesystem, and it would
> work properly on a guest system that had /data? Do I need to unmount the
> filesystem, or shut down the guest VM, or mount the guest from a LiveCD?
I think you must reboot the guest to see the new bigger disk, then you
can repartition, and then after another reboot you can resize your fs.
Kind Regards, Markus Falb
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