Moving files around within the namespace never changes the way the file data is represented within RADOS. It’s just twiddling metadata bits. :) -Greg On Thu, Jul 6, 2023 at 3:26 PM Dan van der Ster <dan.vanderster@xxxxxxxxx> wrote: > 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 > _______________________________________________ ceph-users mailing list -- ceph-users@xxxxxxx To unsubscribe send an email to ceph-users-leave@xxxxxxx
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