doc: Clean up the snapshot consistency note

The old note made it sound like we weren't crash-consistent, and had a
confusing section about needing to clone before mounting.
You *do* need to clone the snapshot before mounting it, but that has
nothing to do fs freezing or consistency.

Signed-off-by: Greg Farnum <gfarnum@redhat.com>

diff --git a/doc/rbd/rbd-snapshot.rst b/doc/rbd/rbd-snapshot.rst
index 3963a3038bda75cb85c68b13ab80d5d52260e6f4..c52e4041163578e43a362829fc6f410bc43887b6 100644 (file)
--- a/doc/rbd/rbd-snapshot.rst
+++ b/doc/rbd/rbd-snapshot.rst
@@ -14,15 +14,16 @@ command and many higher level interfaces, including `QEMU`_, `libvirt`_,
 
 .. important:: To use use RBD snapshots, you must have a running Ceph cluster.
 
-.. note:: If a snapshot is taken while `I/O` is still in progress in a image, the
-   snapshot might not get the exact or latest data of the image and the snapshot
-   may have to be cloned to a new image to be mountable. So, we recommend to stop
-   `I/O` before taking a snapshot of an image. If the image contains a filesystem,
-   the filesystem must be in a consistent state before taking a snapshot. To stop
-   `I/O` you can use `fsfreeze` command. See `fsfreeze(8)` man page for more details.
-   For virtual machines, `qemu-guest-agent` can be used to automatically freeze
-   filesystems when creating a snapshot.
-   
+.. note:: Because RBD does not know about the filesystem, snapshots are
+         `crash-consistent` if they are not coordinated with the mounting
+         computer. So, we recommend you stop `I/O` before taking a snapshot of
+         an image. If the image contains a filesystem, the filesystem must be
+         in a consistent state before taking a snapshot or you may have to run
+         `fsck`. To stop `I/O` you can use `fsfreeze` command. See
+         `fsfreeze(8)` man page for more details.
+         For virtual machines, `qemu-guest-agent` can be used to automatically
+         freeze filesystems when creating a snapshot.
+
 .. ditaa:: +------------+         +-------------+
            | {s}        |         | {s} c999    |
            |   Active   |<-------*|   Snapshot  |