Reclaim disk space from a sparse image file qcow2/ vmdk

Sparse disk image formats such as qcow2 only consume the physical disk space which they need. For example, if a guest is given a qcow2 image with a size of 100GB but has only written to 10GB then only 10GB of physical disk space will be used. There is some slight overhead associated, so the above example may not be strictly true, but you get the idea.

Sparse disk image files allow you to over allocate virtual disk space – this means that you could allocate 5 virtual machines 100GB of disk space, even if you only have 300GB of physical disk space. If all the guests need 100% of their 100GB disk space then you will have a problem. If you use over allocation of disk space you will need to monitor the physical disk usage very carefully.

There is another problem with sparse disk formats, they don’t automatically shrink. Let’s say you fill 100GB of a sparse disk (we know this will roughly consume 100GB of physical disk space) and then delete some files so that you are only using 50GB. The physical disk space used should be 50GB, right? Wrong. Because the disk image doesn’t shrink, it will always be 100GB on the file system even if the guest is now using less. The below steps will detail how to get round this issue. Continue reading “Reclaim disk space from a sparse image file qcow2/ vmdk” »


Install Qemu Guest Agent on Proxmox

The qemu-guest-agent is a helper daemon, which is installed in the guest. It is used to exchange information between the host and guest, and to execute command in the guest.

In Proxmox VE, the qemu-guest-agent is used for mainly two things:

  • To properly shutdown the guest, instead of relying on ACPI commands or windows policies
  • To freeze the guest file system when making a backup (on windows, use the volume shadow copy service VSS).

Installation Host
You have to enable the guest-agent per VM, either set it in the GUI to “Yes” under options (see screenshot):

or via CLI:

qm set VMID --agent 1

Guest Linux
On Linux you have to simply install the qemu-guest-agent, please refer to the documentation of your system.

We show here the commands for Debian/Ubuntu and Redhat based systems:

Continue reading “Install Qemu Guest Agent on Proxmox” »