Hello Peter, thank you so much for that detailed info! Sorry, you were right, when trying to delete my external snapshot via snapshot-delete, the error says "deletion of external snapshots unsupported"
I can't merge the snapshot because the VM image is in a read-only filesystem. Sorry I should've said, it's a live system. So the image is in the read-only squashfs and external snapshot in overlay is used for writing. Now I would like the snapshot emptied or deleted/recreated when it reaches 4GB. Is there even a way to do this with the image being read-only? Thanks again for your advice, I really love this community. On Tue, Nov 30, 2021, 9:42 AM Peter Krempa <pkre...@redhat.com> wrote: > On Mon, Nov 29, 2021 at 13:05:40 +0100, Elias Mobery wrote: > > Hi everybody! > > > > I'm using a snapshot purely for writes and was wondering if it's possible > > to clear/empty the snapshot after it reaches a certain size? > > > > Created with: > > virsh snapshot-create-as --disk-only > > So this creates a so-called external snapshot, which for disks means an > overlay image. > > > > > I tried deleting and recreating it but get an error at deletion: > > > > virsh snapshot-delete > > but unfortunately deleting external snapshots is not yet implemented. > > The usual approach is to do a block commit operation to merge the > overlay images back into the backing image manually. > > The basic syntax via virsh is: > > virsh blockcommit --active --pivot --verbose $VM $DISK > > This merges any overlay images into the backing image. Backing image is > the most deepest nested image when you look at <backingStore> in the > XML. > > > Error: source for disk 'vda' is not a regular file > > This error doesn't make much sense though. The error should state that > deletion of external snapshots is nto supported. > > > > > I also tried virsh snapshot-create-as --no-metadata --disk-only > > This creates a snapshot without libvirt metadata. This means that > libvirt just creates the overlay, but doesn't create any internal state > related to it. > > It saves you the step of deleting metadata, but you still need to > manually merge the image. > > > > > But the same error as above pops up when trying to delete. > > This makes absolutely no sense though. Are you sure you are copying the > correct error message? 'virsh snapshot-delete' works _only_ with > snapshots which do have metadata, so if you create a snapshot without > there's nothing to delete. > >
