Is this reintroduced? I am on version 2.3.0
$ dd if=/dev/urandom of=disk bs=1M count=1024
$ qemu-img convert -f raw -O qcow2 disk disk.qcow
$ qemu-img convert -f raw -O qcow2 -o backing_file=disk.qcow disk
disk1.qcow
$ ls -l
total 3146388
-rw-r--r-- 1 sakis sakis 1073741824 10 авг 15,29 disk
-rw-r--r-- 1 sakis sakis 1074135040 10 авг 15,30 disk.qcow
-rw-r--r-- 1 sakis sakis 1074135040 10 авг 15,31 disk1.qcow
All the data is copied again.
$ qemu-img info disk1.qcow
image: disk1.qcow
file format: qcow2
virtual size: 1.0G (1073741824 bytes)
disk size: 1.0G
cluster_size: 65536
*backing file: disk.qcow*
Format specific information:
compat: 1.1
lazy refcounts: false
refcount bits: 16
corrupt: false
Qemu-img works as expected though.
$ qemu-img create -f qcow2 -o backing_file=disk1.qcow disk2.qcow
$ ls -l
total 3146584
-rw-r--r-- 1 sakis sakis 1073741824 10 авг 15,29 disk
-rw-r--r-- 1 sakis sakis 1074135040 10 авг 15,30 disk.qcow
-rw-r--r-- 1 sakis sakis 1074135040 10 авг 15,31 disk1.qcow
-rw-r--r-- 1 sakis sakis 197120 10 авг 15,33 disk2.qcow
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https://bugs.launchpad.net/bugs/660366
Title:
"qemu-img convert -O qcow2 -o backing_file" makes huge images
Status in QEMU:
Fix Released
Bug description:
$ dd if=/dev/urandom bs=1M of=1.img count=4
4+0 records in
4+0 records out
4194304 bytes (4,2 MB) copied, 1,0413 s, 4,0 MB/s
$ qemu-img create -f qcow2 -b 1.img 2.img
Formatting '2.img', fmt=qcow2 size=4194304 backing_file='1.img'
encryption=off cluster_size=0
$ qemu-img convert -O qcow2 -o backing_file=1.img 2.img 3.img
$ du -h ?.img
4,1M 1.img
144K 2.img
4,3M 3.img
The conversion result is bigger then the source!
It appears that "-o backing_file" is not applied to data (as
expected). I.e. all data is put into the resulting image: both from
source image and "backing" image.
Expected behavior is to put only data that is not present in
backing_file.
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