doc: rbd-mirroring: Explain snapshot mirroring

* Rectify that snapshot based mirroring is point-in-time consistent
* Reword slightly s.t. there is less repetition.

Based on the discussion in https://lists.ceph.io/hyperkitty/list/ceph-users@ceph.io/thread/G6ZW5OP4IXGUBAJTKZDPABK7HCKYISQH/

Signed-off-by: Hans van den Bogert <hansbogert@gmail.com>

diff --git a/doc/rbd/rbd-mirroring.rst b/doc/rbd/rbd-mirroring.rst
index 9e83aa58baee5879fe182444163fe6b75a9d05be..8315a89132f25d10510f51ae80c4cb70bba53e99 100644 (file)
--- a/doc/rbd/rbd-mirroring.rst
+++ b/doc/rbd/rbd-mirroring.rst
@@ -21,10 +21,10 @@ capability is available in two modes:
   updates between two mirror-snapshots and copy the deltas to its local copy of
   the image. With the help of the RBD fast-diff image feature, updated data
   blocks can be quickly computed without the need to scan the full RBD image.
-  Since this mode is not point-in-time consistent, the full snapshot delta will
-  need to be synced prior to use during a failover scenario. Any partially
-  applied snapshot deltas will be rolled back to the last fully synced snapshot
-  prior to use.
+  Since this mode is not as fine-grained as journaling, the complete delta 
+  between two snapshots will need to be synced prior to use during a failover
+  scenario. Any partially applied set of deltas will be rolled back at moment
+  of failover.
 
 .. note:: journal-based mirroring requires the Ceph Jewel release or later;
    snapshot-based mirroring requires the Ceph Octopus release or later.