New qcow2 hard allocated size... fixed size ?

[Pascal.G]

Hi,

I noticed freshly created qcow2 disks (created from web interface) takes really the maximum size expected (all space specified is pre-allocated). While, new created ones (using qemu-img create) are created correctly...(growable)...

Can you please confirm me this ?

Nb : proxmox 2.2 updated ok on 23/11/2012

Best regards
Pascal G.

 

[dietmar]

We peallocate metadata now (bu the file is still sparse).

 

[spirit]

yes, file is sparse.
Do a "df" after creating the file, you'll see that free space is not taken by image.

 

[sigxcpu]

Then what is the difference between qcow2 and sparse .img files?
qcow2 has the big advantage to be easily copied between storage points (e.g. scripts for cloning a KVM template). cp --sparse is not an option, because it "reads" zero-filled block, which takes a lot of time (e.g. 750GB virtual qcow2 disk in template).

 

[dietmar]

file with preallocate metadata are faster.

 

[Pascal.G]

Many thanks to all

 

[sigxcpu]

For big, fast sparse files we have raw .img, which are even faster, being simpler.

Is there any fast method left to transfer a metadata-prealloc'd QCOW2 file from one location to another now?

 

[osaluden]

Hi all, thank you for your answers and congratulation for this useful forum.
Regarding qcow2 files with prealocated metadata : I created VM with a 20 GB qcow2 virtual disk. The "ls" command show me that the file is 20GB and the "df" show that these 20GB are not allocated : all right. Now, I backup this VM (stopped VM and gzip format), the backup is about 1.3GB (depends on the OS installed in). When I restore this VM, the qcow2 file is 20GB ("ls" confirmed) BUT the "df" shows me that 20GB are now allocated .
So there is a difference between creating a qcow2 VM based (auto-extend qcow2 file) and restoring this VM (qcow2 fixed size file).
Could you please explain me this behavior ? Is there a way to restore a qcow2 based VM with an auto-extend qcow2 file (like the original one before restoration) ?

 

[dietmar]

Could you please explain me this behavior?

This will be fixed in 2.3

Is there a way to restore a qcow2 based VM with an auto-extend qcow2 file (like the original one before restoration) ?

Try 'qemu-img convert' to copy data into a new qcow 2 file.

 

[osaluden]

When I restore a qcow2 based VM, the qcow2 file size is fully allocated onto the FS whereas the original qcow2 file size is dynamic (auto-extend qcow2). Why ?

 

[spirit]

When I restore a qcow2 based VM, the qcow2 file size is fully allocated onto the FS whereas the original qcow2 file size is dynamic (auto-extend qcow2). Why ?

Maybe restore fill the gap with zero ?

Dietmar is currently working on a new backup solution,which should handle that . (live backup for all storages type without snapshots), It should coming soon.

 

[osaluden]

Thanks a lot for your answers ! Sorry for posting the same questions twice, I thought my first question was not published ...
Indeed, I already tryed the "qemu-convert" : the new generated qcow2 file is an auto-extend file but without prealocated metadata; as a result the I/O write on this new virtual HDD are very bad (compare to a prealocated metadata qcow2 file).
So, let's wait for 2.3 version ! (this will prevent us to manually convert qcow2 file into a poor I/O qcow2 file after a restoration)

Congratulations for this great product !

 

[osaluden]

Hi, do you know when PVE 2.3 will be available ? It is not mentionned within the PVE roadmap.

Thanks in advance for your answer.

 

[tom]

all releases will be announce in this forum and in the announcement forum.