On Thu, Jun 8, 2017 at 3:33 PM, McFarland, Bruce <Bruce.McFarland@xxxxxxxxxxxx> wrote: > John, > > Thanks for your answers. I have a clarification on my questions see below > inline. > > Bruce > > > > From: John Spray <jspray@xxxxxxxxxx> > Date: Thursday, June 8, 2017 at 1:45 AM > To: "McFarland, Bruce" <Bruce.McFarland@xxxxxxxxxxxx> > Cc: "ceph-users@xxxxxxxxxxxxxx" <ceph-users@xxxxxxxxxxxxxx> > Subject: Re: CephFS Snapshot questions > > > > On Wed, Jun 7, 2017 at 11:46 PM, McFarland, Bruce > > <Bruce.McFarland@xxxxxxxxxxxx> wrote: > > I have a couple of CephFS snapshot questions > > > > - Is there any functionality similar to rbd clone/flatten such that > > the snapshot can be made writable? Or is that as simple as copying the > > .snap/<dirname> to another cluster? > > > > No, there's no cloning. You don't need another cluster though -- you > > can "cp -r" your snapshot anywhere on any filesystem, and you'll end > > up with fresh files that you can write to. > > > > > > - If the first object write since the snapid was created is a user > > error how is that object recovered if it isn’t added to the snapid until > > it’s 1st write after snapid creation? > > > > Don't understand the question at all. "user error"? > > > > I think I’ve answered this for myself. The case would be a user’s first > write to an object after the snap is created being an error they wanted to > “fix” by restoring the object from the objects clone. So when the user > writes the “error” to the object it is copied to the snap while it is also > being written. The object can then be restored from the clone in this case > where the first write to it is in error and it can be recovered from its > clone which hadn’t been populated with that object until that write. It seems like you're imagining a situation where we do COW at the CephFS layer? We don't do that. The snapshot stuff is all implemented at a lower level, and exactly how it works is up to the disk store. What you see as a user of CephFS is just the snapshotted file and the current revision of the file -- when you want to restore something, you do it by over-writing the current revision from the snapshot. > - If I want to clone the .snap/<dirname>/ and not all objects have > > been written since .snap/<dirname>/ was created how do I know if or get all > > objects into the snap if I wanted to move the snap to another cluster? > > > > There's no concept of moving a snapshot between clusters. If you're > > just talking about doing a "cp -r" of the snapshot, then the MDS > > should do the right thing in terms of blocking your reads on files > > that have dirty data in client caches -- when we make a snapshot then > > clients doing buffered writes are asked to flush those buffers. > > > > There are 2 cases I’m wondering about here that I didn’t accurately > describe. 1 would be data migration between clusters which might not be > possible and 2 would be storing clones on a second cluster. > > 1. Is it possible to snap a directory tree on its source cluster and > then copy it to a new/different destination cluster? Would that be > prohibited due to the snaps MDS being on the source cluster? I can see that > being useful for migrating data/users between clusters, but that it might > not be possible. You can copy around the files from snapshots, but the snapshots themselves are not something that's import/exportable. > > 2. I would expect this to be possible where a snap is created, it’s > then compressed into a tarball, and that tarball is stored on a second > cluster for any future DR at which point it’s copied back to the source > cluster, extracted restoring directory tree to state at time of snap > creation. You can totally do this -- it's all just files, from the point of view of a tool like tar. John > > > > John > > > > > > > > I might not be making complete sense yet and am in the process of testing to > > see how CephFS snapshots behave. > > > > > > > > > > _______________________________________________ > > ceph-users mailing list > > ceph-users@xxxxxxxxxxxxxx > > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > > > > _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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