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me,apporc

2013-Apr-12 09:25 UTC

[libvirt-users] after snapshot-delete, the qcow2 image file size doesn't decrease

After snapshot-delete, the qcow2 image file size doesn't decrease, isn't
that a waste of disk space?
Would someone please tell me how to decrease the file size when
snapshot-delete, if that's possible?


The image file name of my virtual machine is d0.qcow
As follows:

[root at test1 ]# virsh list
 Id    Name                           State
----------------------------------------------------

 32    bfbe8ca8-8579-11e2-844a-001018951f48 running


[root at test1 ]# qemu-img info d0.qcow
image: d0.qcow
file format: qcow2
virtual size: 8.0G (8589934592 bytes)
disk size: 3.6G
cluster_size: 65536
[root at test1 ]# ls -lh
total 3.6G
-rw------- 1 qemu qemu 3.6G Apr 12 17:13 d0.qcow
drwx------ 2 root root 4.0K Apr 12 17:12 held
[root at test1 ]# virsh snapshot-list bfbe8ca8-8579-11e2-844a-001018951f48
 Name                 Creation Time             State
------------------------------------------------------------

[root at test1 8]# virsh snapshot-create bfbe8ca8-8579-11e2-844a-001018951f48
Domain snapshot 1365758005 created
[root at test1 ]# virsh snapshot-create bfbe8ca8-8579-11e2-844a-001018951f48
Domain snapshot 1365758022 created
[root at test1 bfbe8ca8-8579-11e2-844a-001018951f48]# virsh snapshot-list
bfbe8ca8-8579-11e2-844a-001018951f48
 Name                 Creation Time             State
------------------------------------------------------------
 1365758005           2013-04-12 17:13:25 +0800 running
 1365758022           2013-04-12 17:13:42 +0800 running

[root at test1 ]# qemu-img info d0.qcow
image: d0.qcow
file format: qcow2
virtual size: 8.0G (8589934592 bytes)
disk size: 3.8G
cluster_size: 65536
Snapshot list:
ID        TAG                 VM SIZE                DATE       VM CLOCK
1         1365758005             127M 2013-04-12 17:13:25   00:00:53.141
2         1365758022             127M 2013-04-12 17:13:42   00:01:09.508
[root at test1 ]# ls -lh
total 3.9G
-rw------- 1 qemu qemu 3.9G Apr 12 17:14 d0.qcow
drwx------ 2 root root 4.0K Apr 12 17:12 held
[root at test1 ]# virsh snapshot-delete
bfbe8ca8-8579-11e2-844a-001018951f48 1365758022
Domain snapshot 1365758022 deleted

[root at test1 ]# qemu-img info d0.qcow
image: d0.qcow
file format: qcow2
virtual size: 8.0G (8589934592 bytes)
disk size: 3.8G
cluster_size: 65536
Snapshot list:
ID        TAG                 VM SIZE                DATE       VM CLOCK
                                    0 1970-01-01 08:00:00   00:00:00.000
[root at test1 ]# ls -lh
total 3.9G
-rw------- 1 qemu qemu 3.9G Apr 12 17:14 d0.qcow
drwx------ 2 root root 4.0K Apr 12 17:12 held
[root at test1 ]# virsh snapshot-delete
bfbe8ca8-8579-11e2-844a-001018951f48 1365758005
Domain snapshot 1365758005 deleted

[root at test1 ]# qemu-img info d0.qcow
image: d0.qcow
file format: qcow2
virtual size: 8.0G (8589934592 bytes)
disk size: 3.8G
cluster_size: 65536
[root at test1 ]# ls -lh
total 3.9G
-rw------- 1 qemu qemu 3.9G Apr 12 17:14 d0.qcow
drwx------ 2 root root 4.0K Apr 12 17:12 held
[root at test1 ]# virsh snapshot-create bfbe8ca8-8579-11e2-844a-001018951f48
Domain snapshot 1365758311 created
[root at test1 ]# qemu-img info d0.qcow
image: d0.qcow
file format: qcow2
virtual size: 8.0G (8589934592 bytes)
disk size: 3.8G
cluster_size: 65536
Snapshot list:
ID        TAG                 VM SIZE                DATE       VM CLOCK
1         1365758311             252M 2013-04-12 17:18:32   00:05:58.136
[root at test1 ]# ls -lh
total 3.9G
-rw------- 1 qemu qemu 3.9G Apr 12 17:18 d0.qcow
drwx------ 2 root root 4.0K Apr 12 17:12 held
[root at test1 ]# virsh snapshot-create bfbe8ca8-8579-11e2-844a-001018951f48
Domain snapshot 1365758338 created
[root at test1 ]# qemu-img info d0.qcow
image: d0.qcow
file format: qcow2
virtual size: 8.0G (8589934592 bytes)
disk size: 4.1G
cluster_size: 65536
Snapshot list:
ID        TAG                 VM SIZE                DATE       VM CLOCK
1         1365758311             252M 2013-04-12 17:18:32   00:05:58.136
2         1365758338             252M 2013-04-12 17:18:58   00:06:24.272
[root at test1 ]# ls -lh
total 4.1G
-rw------- 1 qemu qemu 4.1G Apr 12 17:19 d0.qcow
drwx------ 2 root root 4.0K Apr 12 17:12 held
[root at test1 ]# virsh snapshot-list bfbe8ca8-8579-11e2-844a-001018951f48
 Name                 Creation Time             State
------------------------------------------------------------
 1365758311           2013-04-12 17:18:31 +0800 running
 1365758338           2013-04-12 17:18:58 +0800 running

[root at test1 ]# qemu-img info d0.qcow
image: d0.qcow
file format: qcow2
virtual size: 8.0G (8589934592 bytes)
disk size: 4.1G
cluster_size: 65536
Snapshot list:
ID        TAG                 VM SIZE                DATE       VM CLOCK
1         1365758311             252M 2013-04-12 17:18:32   00:05:58.136
2         1365758338             252M 2013-04-12 17:18:58   00:06:24.272
[root at test1 ]# virsh snapshot-delete
bfbe8ca8-8579-11e2-844a-001018951f48 1365758338
Domain snapshot 1365758338 deleted

[root at test1 ]# qemu-img info d0.qcow
image: d0.qcow
file format: qcow2
virtual size: 8.0G (8589934592 bytes)
disk size: 4.1G
cluster_size: 65536
Snapshot list:
ID        TAG                 VM SIZE                DATE       VM CLOCK
1         1365758311             252M 2013-04-12 17:18:32   00:05:58.136
[root at test1 ]# ls -lh
total 4.1G
-rw------- 1 qemu qemu 4.1G Apr 12 17:20 d0.qcow
drwx------ 2 root root 4.0K Apr 12 17:12 held
[root at test1 ]# virsh snapshot-delete
bfbe8ca8-8579-11e2-844a-001018951f48 1365758311
Domain snapshot 1365758311 deleted

[root at test1 ]# qemu-img info d0.qcow
image: d0.qcow
file format: qcow2
virtual size: 8.0G (8589934592 bytes)
disk size: 4.1G
cluster_size: 65536
[root at test1 ]# ls -lh
total 4.1G
-rw------- 1 qemu qemu 4.1G Apr 12 17:20 d0.qcow
drwx------ 2 root root 4.0K Apr 12 17:12 held
[root at test1 ]# virsh snapshot-list bfbe8ca8-8579-11e2-844a-001018951f48
 Name                 Creation Time             State
------------------------------------------------------------
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Daniel P. Berrange

2013-Apr-12 09:53 UTC

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[libvirt-users] after snapshot-delete, the qcow2 image file size doesn't decrease

On Fri, Apr 12, 2013 at 05:25:23PM +0800, me,apporc
wrote:> After snapshot-delete, the qcow2 image file size doesn't decrease,
isn't
> that a waste of disk space?
Yes, but that's life. When deleting an internal qcow2 snapshot,
QEMU will just mark the clusters as unused, it won't return them
to the underlying filesystem. These unused clusters will, however,
be re-used if the qcow2 file needs to grow later.
> Would someone please tell me how to decrease the file size when
> snapshot-delete, if that's possible?
You can't do it in place. The only option would be to use qemu-img
to clone the qcow2 file to a new qcow2 file & delete the original.

Daniel
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