From 505025c64153ec47b9a9aa3a25a91d4059cd7bc4 Mon Sep 17 00:00:00 2001 From: Greg Farnum Date: Thu, 20 Dec 2018 10:33:38 -0800 Subject: [PATCH] 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 --- doc/rbd/rbd-snapshot.rst | 19 ++++++++++--------- 1 file changed, 10 insertions(+), 9 deletions(-) diff --git a/doc/rbd/rbd-snapshot.rst b/doc/rbd/rbd-snapshot.rst index 3963a3038bda7..c52e404116357 100644 --- 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 | -- 2.39.5