On Wed, Jun 24, 2020 at 09:23:00 -0500, Eric Blake wrote: > On 6/24/20 9:07 AM, Peter Krempa wrote: > > Make it obvious what's meant by 'overlay' and 'backing image' for sake > > of extension of the document. > > > > Signed-off-by: Peter Krempa <pkrempa@xxxxxxxxxx> > > --- > > docs/kbase/incrementalbackupinternals.rst | 15 +++++++++++++++ > > 1 file changed, 15 insertions(+) > > Reviewed-by: Eric Blake <eblake@xxxxxxxxxx> > > > > > diff --git a/docs/kbase/incrementalbackupinternals.rst b/docs/kbase/incrementalbackupinternals.rst > > index 0c4b4f7486..eada0d2935 100644 > > --- a/docs/kbase/incrementalbackupinternals.rst > > +++ b/docs/kbase/incrementalbackupinternals.rst > > @@ -94,6 +94,21 @@ so, even if we obviously can't guarantee that. > > Integration with external snapshots > > =================================== > > > > +External snapshot terminology > > +----------------------------- > > + > > +External snapshots on a disk level consist of layered chains of disk images. An > > +image in the chain can have a ``backing image`` placed below. Any chunk in the > > +current image which was not written explicitly is transparent and if read the > > +data from the backing image is passed through. An image placed on top of the > > +current image is called ``overlay``. > > + > > +The bottommost backing image at the end of the chain is also usually described > > +as ``base image``. > > + > > +The topmost overlay is the image which is being written to by the VM and is also > > +described as the ``active`` layer or image. > > Maybe it's also worth a paragraph mentioning how diagramming the chains we > typically use <- for 'Backed by', as in: > > Base <- Top Good idea! I'll follow up with a patch to add the paragraph.
