On Tue, Nov 24, 2015 at 01:40:28PM +0000, Richard W.M. Jones wrote: > On Tue, Nov 24, 2015 at 02:30:42PM +0200, Yaniv Kaul wrote: > > Assuming the VM is not running, and we have a base (raw, sparse) with a > > snapshot (qcow2) on top of it. > > Is there any issue with running virt-sparsify on the base image? I assume > > deleted blocks in the base can be sparsified, since they are either still > > deleted on the snap (which is fine) or were written in the snap (which is > > fine either and does not change or matter for the base image). > > It could fail very badly (corrupting data), in at least the following > situation: > > - Base image has Linux filesystems that require journal recovery > (eg. they were not unmounted, the VM was not shut down cleanly, or > they represent a snapshot of a running system) > > - virt-sparsify --inplace will do: > > for each fs: > mount fs /sysroot > fstrim /sysroot > > - The mount command will replace the journal, making arbitrary > changes to the base image.
s/replace/replay/ > - The snapshot will not know about these changes, resulting in disk > corruption when you try to access the VM via the snapshot. > > virt-sparsify copying mode would do something similar. > > There may be other situations where it could fail. Definitely don't do it :-) > > > Can I assume sparsifying should not make any changes that matter for a VM > > that will be spun (post the process)? > > spun? > > Rich. > > -- > Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones > Read my programming and virtualization blog: http://rwmj.wordpress.com > virt-top is 'top' for virtual machines. Tiny program with many > powerful monitoring features, net stats, disk stats, logging, etc. > http://people.redhat.com/~rjones/virt-top -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-top is 'top' for virtual machines. Tiny program with many powerful monitoring features, net stats, disk stats, logging, etc. http://people.redhat.com/~rjones/virt-top _______________________________________________ Libguestfs mailing list [email protected] https://www.redhat.com/mailman/listinfo/libguestfs
