Hi all, I understood that the watcher cannot prevent multiple mounts. Based on the feedback I received, I will consider countermeasures.
Thank you for your valuable insights. Yuma. 2024年5月23日(木) 21:15 Frank Schilder <fr...@dtu.dk>: > > Hi, we run into the same issue and there is actually another use case: > live-migration of VMs. This requires an RBD image being mapped to two clients > simultaneously, so this is intentional. If multiple clints map an image in > RW-mode, the ceph back-end will cycle the write lock between the clients to > allow each of them to flush writes, this is intentional. The way to > coordinate here is the job of the orchestrator. In this case specifically, > its explicitly managing a write lock during live-migration such that writes > occur in the correct order. > > Its not a ceph job, its an orchestration job. The rbd interface just provides > the tools to do it, for example, you can attach information that helps you > hunting down dead-looking clients and kill them proper before mapping an > image somewhere else. > > Best regards, > ================= > Frank Schilder > AIT Risø Campus > Bygning 109, rum S14 > > ________________________________________ > From: Ilya Dryomov <idryo...@gmail.com> > Sent: Thursday, May 23, 2024 2:05 PM > To: Yuma Ogami > Cc: ceph-users@ceph.io > Subject: [ceph-users] Re: does the RBD client block write when the Watcher > times out? > > On Thu, May 23, 2024 at 4:48 AM Yuma Ogami <yuma.ogami.cyb...@gmail.com> > 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 > _______________________________________________ > ceph-users mailing list -- ceph-users@ceph.io > To unsubscribe send an email to ceph-users-le...@ceph.io _______________________________________________ ceph-users mailing list -- ceph-users@ceph.io To unsubscribe send an email to ceph-users-le...@ceph.io
