On Thu, May 23, 2024 at 4:48 AM Yuma Ogami <yuma.ogami.cybozu@xxxxxxxxx> wrote:
>
> Hello.
>
> I'm currently verifying the behavior of RBD on failure. I'm wondering
> about the consistency of RBD images after network failures. As a
> result of my investigation, I found that RBD sets a Watcher to RBD
> image if a client mounts this volume to prevent multiple mounts. In
Hi Yuma,
The watcher is created to watch for updates (technically, to listen to
notifications) on the RBD image, not to prevent multiple mounts. RBD
allows the same image to be mapped multiple times on the same node or
on different nodes.
> addition, I found that if the client is isolated from the network for
> a long time, the Watcher is released. However, the client still mounts
> this image. In this situation, if another client can also mount this
> image and the image is writable from both clients, data corruption
> occurs. Could you tell me whether this is a realistic scenario?
Yes, this is a realistic scenario which can occur even if the client
isn't isolated from the network. If the user does this, it's up to the
user to ensure that everything remains consistent. One use case for
mapping the same image on multiple nodes is a clustered (also referred
to as a shared disk) filesystem, such as OCFS2.
Thanks,
Ilya
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