Standard and default images create using virt-manager on linux, automatically full allocating specified disk size to host. To avoid un-usable disk space, you should avoid choosing default images created by virt-manager.

->Creating VM's disk using Virt Manager<-

To create growing images files for VM’s, I choose qcow2. Why growing images? To ensure the host only allocated how much diskspace to harddrive (fill-as-you-go), not how big the disk was allocated. For example :

$ sudo qemu-img create -f qcow2 100G
Formatting '', fmt=qcow2 size=107374182400 encryption=off cluster_size=65536 lazy_refcounts=off

It should be create qcow2 files and have following information:

$ sudo qemu-img info
file format: qcow2
virtual size: 100G (107374182400 bytes)
disk size: 196K
cluster_size: 65536
Format specific information:
    compat: 1.1
    lazy refcounts: false

See at disk size, we have only 196K on first init. For sure, let’s check it.

$ ls -lah
-rw-r--r--. 1 dmnQ dmnQ 194K Oct 13 03:35

And it will save your disk space as much as you want, and will growth as the data growth. Then after creating the disk file, you need to load it on virt-manager by choosing Select or create custom storage.

->Select or create custom storage<-

Done, now you have optimized qcow2 files and growth as the data growth.

Dewangga Alam

Father, Husband, and an Engineer!