[Openstack-operators] Reducing ext4/qcow2 snapshot size

Lloyd Dewolf lloydostack at gmail.com
Tue Aug 21 16:47:27 UTC 2012

On Mon, Aug 20, 2012 at 6:04 PM, Lorin Hochstein
<lorin at nimbisservices.com> wrote:
> On Aug 20, 2012, at 12:47 PM, Samuel Winchenbach <swinchen at gmail.com> wrote:
> Hi all,
> I launched a large (100 GB) VM and made the changes I wanted
> (installed software, created users, etc...)  and made a snapshot.
> Now I would like to launch VMs from that snapshot with a smaller disk
> size, but no mater what flavor I select it always creates a 100GB
> image.
> Is there a way to reduce the ext4 partition size inside the qcow2 disk
> image?   It might involve creating a new image file and cloning over
> the original image?  If so what tools do you use for the cloning?
> Sam:
> You can mount the qcow2 image in your file system using qemu-nbd (see
> http://en.wikibooks.org/wiki/QEMU/Images#Mounting_an_image_on_the_host) and
> then resize the partition using the e2fsprogs tools (e.g., see
> http://en.positon.org/post/Resize-an-ext3-ext4-partition).
> I believe you can also use libguestfs <http://libguestfs.org/> as an
> alternative to qemu-nbd, but I've never tried it.

When last I looked qcow2 images could be shrunk, so although you can
shrink the filesystems you won't fully benefit from the smaller size
as the first instance will be raw'd to the full size.


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