Re: [libvirt-users] Create qcow2 v3 volumes via libvirt

On 05/01/2018 04:17 PM, Paul O'Rorke wrote: > I have been using internal snapshots on production qcow2 images for a > couple of years, admittedly as infrequently as possible with one > exception and that exception has had multiple snapshots taken and > removed using virt-manager's GUI. > > I was unaware of this: >> There are some technical downsides to >> internal snapshots IIUC, such as inability to free the space used by >> the >> internal snapshot when it is deleted, This is not an insurmountable difficulty, just one that no one has spent time coding up. > > This might explain why this VM recently kept going into a paused > state and I had to extend the volume to get it to stay up.  This VM > is used for testing our software in SharePoint and we make heavy use > of snapshots.  Is there nothing I can to do recover that space? If you have no internal snapshots, you can do a 'qemu-img convert' to copy just the portion of the image that is actively in use; the copy will use less disk space than the original because it got rid of the now-unused space.  'virt-sparsify' from libguestfs takes this one step further, by also removing unused space within the guest filesystem itself. In fact, even if you do have internal snapshots, there is probably a sequence of 'qemu-img convert' invocations that can ultimately convert all of your internal snapshots into an external chain of snapshots; but I don't have a ready formula off-hand to point to (experiment on an image you don't care about, before doing it on your production image). > What would be the best practice then for a VM that needs to be able > to create and remove snapshots on a regular basis? In a managed environment, external snapshots probably have the most support for creating and later merging portions of a chain of snapshots, although we could still improve libvirt to make this feel like more of a first class citizen.