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kbase: incrementalbackupinternals: Add snapshot terminology 

Make it obvious what's meant by 'overlay' and 'backing image' for sake
of extension of the document.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
This commit is contained in:
Peter Krempa 2020-06-24 10:56:20 +02:00
parent 8c6dba054b
commit 19061038a7
1 changed files with 15 additions and 0 deletions
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docs/kbase/incrementalbackupinternals.rst
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@ -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.
Handling of bitmaps
-------------------