On Sun, Apr 14, 2019 at 9:20 AM Stefano Garzarella <sgarz...@redhat.com> wrote: > > On Thu, Apr 11, 2019 at 01:06:49PM -0400, Jason Dillaman wrote: > > On Thu, Apr 11, 2019 at 9:02 AM Stefano Garzarella <sgarz...@redhat.com> > > wrote: > > > > > > On Thu, Apr 11, 2019 at 08:35:44AM -0400, Jason Dillaman wrote: > > > > On Thu, Apr 11, 2019 at 7:00 AM Stefano Garzarella > > > > <sgarz...@redhat.com> wrote: > > > > > > > > > > RBD APIs don't allow us to write more than the size set with > > > > > rbd_create() > > > > > or rbd_resize(). > > > > > In order to support growing images (eg. qcow2), we resize the image > > > > > before RW operations that exceed the current size. > > > > > > > > What's the use-case for storing qcow2 images within a RBD image? RBD > > > > images are already thinly provisioned, they support snapshots, they > > > > can form a parent/child linked image hierarchy. > > > > > > > > > > Hi Jason, > > > I understand your point of view, maybe one use case could be if you have > > > a qcow2 image and you want to put it in the rdb pool without convert it. > > > > > > I'm going through this BZ [1] and I'll ask if they have other > > > use cases in mind. > > > > Assuming no good use-cases, perhaps it would just be better to make > > the qemu-img error messages more clear. > > > > Hi Jason, > I asked about use-cases and they want to use qcow2 on rbd in order to > take advantage of these qcow2 features [1]: external snapshots, > Copy-on-write, and optional compression and encryption. > > Maybe the more interesting are external snapshots and Copy-on-write,
Copy-on-write is natively supported by RBD. The concept of external snapshots seems similar to just automating the process of creating a new copy-on-write image. Compression is also supported by Ceph on the cluster side by recent releases. > since encryption can be achieved with LUKS and rbd should support > compression for a specified pool. > > [1] https://bugzilla.redhat.com/show_bug.cgi?id=1171007#c13 > > Cheers, > Stefano -- Jason
