[SOLVED] kvm : cloned image size is MUCH smaller!

fanoflq · 03-29-2017, 12:57 PM

I cloned a VM in KVM using this command:

Code:

# virt-clone --original centos7-1024ram-minimal \
           --auto-clone  \
	--name centos7-1024ram-minimal-clone0

And when I looked at resulting image size, it is MUCH MUCH smaller!
But it runs fine.

Code:

root@server /var/lib/libvirt/images # ls -alh
total 38G
drwx--x--x 2 root         root 4.0K Mar 28 12:55 .
drwxr-xr-x 7 root         root 4.0K Mar 28 16:15 ..
-rw------- 1 libvirt-qemu kvm  1.5G Mar 29 11:44 centos7-1024ram-minimal-clone0.qcow2
-rw------- 1 root         root 2.2G Mar 20 12:52 centos7-1024ram-minimal-clone.qcow2
-rw------- 1 root         root  15G Mar 14 10:07 centos7-1024ram-minimal.qcow2

Why is the image 10X smaller?
How to make its clone the same image size as original?

Thank you.

Madhu Desai · 03-29-2017, 02:24 PM

Quote:

Originally Posted by fanoflq

I cloned a VM in KVM using this command:

Code:

# virt-clone --original centos7-1024ram-minimal \
           --auto-clone  \
	--name centos7-1024ram-minimal-clone0

And when I looked at resulting image size, it is MUCH MUCH smaller!
But it runs fine.

Code:

root@server /var/lib/libvirt/images # ls -alh
total 38G
drwx--x--x 2 root         root 4.0K Mar 28 12:55 .
drwxr-xr-x 7 root         root 4.0K Mar 28 16:15 ..
-rw------- 1 libvirt-qemu kvm  1.5G Mar 29 11:44 centos7-1024ram-minimal-clone0.qcow2
-rw------- 1 root         root 2.2G Mar 20 12:52 centos7-1024ram-minimal-clone.qcow2
-rw------- 1 root         root  15G Mar 14 10:07 centos7-1024ram-minimal.qcow2

Why is the image 10X smaller?
How to make its clone the same image size as original?

Thank you.

What's the output of this command?

Code:

virsh snapshot-list centos7-1024ram-minimal

rknichols · 03-29-2017, 02:26 PM

Quote:

Originally Posted by fanoflq

Code:

# virt-clone --original centos7-1024ram-minimal \
           --auto-clone  \
	--name centos7-1024ram-minimal-clone0

And when I looked at resulting image size, it is MUCH MUCH smaller!
But it runs fine.

Code:

root@server /var/lib/libvirt/images # ls -alh
total 38G
drwx--x--x 2 root         root 4.0K Mar 28 12:55 .
drwxr-xr-x 7 root         root 4.0K Mar 28 16:15 ..
-rw------- 1 libvirt-qemu kvm  1.5G Mar 29 11:44 centos7-1024ram-minimal-clone0.qcow2
-rw------- 1 root         root 2.2G Mar 20 12:52 centos7-1024ram-minimal-clone.qcow2
-rw------- 1 root         root  15G Mar 14 10:07 centos7-1024ram-minimal.qcow2

My guess is that the original image was built with "Allocate entire disk now" checked for its 15GB image file. When the clone was made, only the space actually used was copied. If you run "qemu-img info" on that file, you'll see that its virtual size is 15GB, and it will grow up to that size as space is needed.

fanoflq · 03-29-2017, 02:48 PM

Quote:

Originally Posted by rknichols

My guess is that the original image was built with "Allocate entire disk now" checked for its 15GB image file. When the clone was made, only the space actually used was copied. If you run "qemu-img info" on that file, you'll see that its virtual size is 15GB, and it will grow up to that size as space is needed.

Code:

# qemu-img info centos7-1024ram-minimal-clone0.qcow2
image: centos7-1024ram-minimal-clone0.qcow2
file format: qcow2
virtual size: 14G (15032385536 bytes)
disk size: 1.4G
cluster_size: 65536
Format specific information:
    compat: 1.1
    lazy refcounts: true
    refcount bits: 16
    corrupt: false

or this:

Quote:

# virsh domstats centos7-1024ram-minimal-clone0 | egrep -i "capacity|physical"
block.0.capacity=15032385536
block.0.physical=1528897536

Thanks.

fanoflq · 03-29-2017, 02:50 PM

Quote:

Originally Posted by mddnix

What's the output of this command?

Code:

virsh snapshot-list centos7-1024ram-minimal

I got nothing!

Code:

# virsh snapshot-list centos7-1024ram-minimal
 Name                 Creation Time             State
------------------------------------------------------------

# virsh snapshot-list centos7-1024ram-minimal-clone0
 Name                 Creation Time             State
------------------------------------------------------------
#

Madhu Desai · 03-29-2017, 03:20 PM

@fanoflq, rknichols is indicating at centos7-1024ram-minimal.qcow2 volume. You need to check for this volume. Check whether block.0.capacity and block.0.physical are same for centos7-1024ram-minimal.

fanoflq · 03-29-2017, 03:24 PM

Quote:

Originally Posted by mddnix

@fanoflq, rknichols is indicating at centos7-1024ram-minimal.qcow2 volume. You need to check for this volume. Check whether block.0.capacity and block.0.physical are same for centos7-1024ram-minimal.

Code:

# virsh domstats centos7-1024ram-minimal | egrep -i "capacity|physical"
  block.0.capacity=15032385536
  block.0.physical=15034941440

Same....almost