Hi Mathias, Provided that both subdirs are within the same snap context (subdirs below where the .snap is created), I would assume that in the mv case, the space usage is not doubled: the snapshots point at the same inode and it is just linked at different places in the filesystem. However, if your cluster and livelihood depends on this being true, I suggest making a small test in a tiny empty cephfs, listing the rados pools before and after mv and snapshot operations to find out exactly which data objects are created. Cheers, Dan ______________________________________________________ Clyso GmbH | Ceph Support and Consulting | https://www.clyso.com On Thu, Jun 22, 2023 at 8:54 AM Kuhring, Mathias < mathias.kuhring@xxxxxxxxxxxxxx> wrote: > Dear Ceph community, > > We want to restructure (i.e. move around) a lot of data (hundreds of > terabyte) in our CephFS. > And now I was wondering what happens within snapshots when I move data > around within a snapshotted folder. > I.e. do I need to account for a lot increased storage usage due to older > snapshots differing from the new restructured state? > In the end it is just metadata changes. Are the snapshots aware of this? > > Consider the following examples. > > Copying data: > Let's say I have a folder /test, with a file XYZ in sub-folder > /test/sub1 and an empty sub-folder /test/sub2. > I create snapshot snapA in /test/.snap, copy XYZ to sub-folder > /test/sub2, delete it from /test/sub1 and create another snapshot snapB. > I would have two snapshots each with distinct copies of XYZ, hence using > double the space in the FS: > /test/.snap/snapA/sub1/XYZ <-- copy 1 > /test/.snap/snapA/sub2/ > /test/.snap/snapB/sub1/ > /test/.snap/snapB/sub2/XYZ <-- copy 2 > > Moving data: > Let's assume the same structure. > But now after creating snapshot snapA, I move XYZ to sub-folder > /test/sub2 and then create the other snapshot snapB. > The directory tree will look the same. But how is this treated internally? > Once I move the data, will there be an actually copy created in snapA to > represent the old state? > Or will this remain the same data (like a link to the inode or so)? > And hence not double the storage used for that file. > > I couldn't find (or understand) anything related to this in the docs. > The closest seems to be the hard-link section here: > https://docs.ceph.com/en/quincy/dev/cephfs-snapshots/#hard-links > Which unfortunately goes a bit over my head. > So I'm not sure if this answers my question. > > Thank you all for your help. Appreciate it. > > Best Wishes, > Mathias Kuhring > > _______________________________________________ > ceph-users mailing list -- ceph-users@xxxxxxx > To unsubscribe send an email to ceph-users-leave@xxxxxxx > _______________________________________________ ceph-users mailing list -- ceph-users@xxxxxxx To unsubscribe send an email to ceph-users-leave@xxxxxxx
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