How to prevent QCOW2 files from growing

[TomTomGo]

Hello everyboy,

I'm playing with QCOW2 files / qm snapshot feature for our VMs and i've noticed that some QCOW2 files can became bigger than the VM HDD defined size.

For example, VM 202 with a 60Gb QCOW2 HDD :

qemu-img info /mnt/pve/nas20/images/202/vm-202-disk-1.qcow2
image: /mnt/pve/nas20/images/202/vm-202-disk-1.qcow2
file format: qcow2
virtual size: 60G (64424509440 bytes)
disk size: 62G
cluster_size: 65536
Format specific information:
    compat: 1.1
    lazy refcounts: false

After shrinking with the wiki method, no problem, the file goes to 19G :

qemu-img info /mnt/pve/nas20/images/202/vm-202-disk-1.qcow2
image: /mnt/pve/nas20/images/202/vm-202-disk-1.qcow2
file format: qcow2
virtual size: 60G (64424509440 bytes)
disk size: 19G
cluster_size: 65536
Format specific information:
    compat: 1.1
    lazy refcounts: false

Is there a way to prevent QCOW2 files from growing, especially when using qm snapshots ?
Is it possible to store the snapshot in a separate file, and merge it to the main file when deleting, like on ESXi ?

Regards,

Thomas

 

[spirit]

Hi,

>>Is there a way to prevent QCOW2 files from growing, especially when using qm snapshots ?
No, this is the nature of snapshot. When you take snapshot, new writes will increase size.

>>Is it possible to store the snapshot in a separate file, and merge it to the main file when deleting, like on ESXi ?

No, currently proxmox use only qcow2 internal snapshots.

 

[TomTomGo]

Hi,

>>Is there a way to prevent QCOW2 files from growing, especially when using qm snapshots ?
No, this is the nature of snapshot. When you take snapshot, new writes will increase size.

>>Is it possible to store the snapshot in a separate file, and merge it to the main file when deleting, like on ESXi ?

No, currently proxmox use only qcow2 internal snapshots.

Okay thanks for the reply.
This is problematic in a production environment because if qcow2 files grows over their designed size, this could fill the DATASTORE (like doing thin provisionning) ...
Is there any plan to use qcow2 external snapshots ?