Re: xattrs on snapshots

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On Tue, Nov 12, 2019 at 6:39 AM Toby Darling <toby@xxxxxxxxxxxxxxxxx> wrote:
>
> Hi Folks
>
> I'm writing a backup/sync process for our ceph cluster. The process
> takes a snapshot of the system that's being backed up and rsync's from
> that to another ceph cluster
>
> I was hoping to use the snapshot xattrs to verify a successful backup by
> comparing ceph.dir.rbytes and ceph.dir.rentries between the snapshot and
> backup target.
>
> However, while files added to the source directory after the snapshot is
> taken don't appear in the snapshot, ceph.dir.rbytes and ceph.dir.rctime
> are updated in the xattrs of both.

I don't remember for sure, but I think you're falling victim to rstat
propagation being lazy here, and metadata in snapshots being somewhat
delayed. Can you try doing a sync before you take the snapshot and see
if that changes the behavior?
-Greg

>
> $ fallocate -l 1K test1
>
> $ getfattr -n ceph.dir.rbytes .
> # file: .
> ceph.dir.rbytes="1024"
>
> $ mkdir .snap/testsnap
>
> $ fallocate -l 2K test2
>
> $ getfattr -n ceph.dir.rbytes . .snap/testsnap
> # file: .
> ceph.dir.rbytes="3072"
>
> # file: .snap/testsnap
> ceph.dir.rbytes="3072"
>
> $ getfattr -n ceph.dir.rctime . .snap/testsnap
> # file: .
> ceph.dir.rctime="1573558448.09736131125"
>
> # file: .snap/testsnap
> ceph.dir.rctime="1573558448.09736131125"
>
> $ tree -a --si . .snap
> .
> |-- [1.0k]  test1
> `-- [2.0k]  test2
> .snap
> `-- [3.1k]  testsnap
>      `-- [1.0k]  test1
>
> 1 directory, 3 files
>
> Have I misunderstood? Is this expected behaviour?
>
> Cheers
> Toby
> --
> Toby Darling, Scientific Computing (2N249)
> MRC Laboratory of Molecular Biology
> Francis Crick Avenue
> Cambridge Biomedical Campus
> Cambridge CB2 0QH
> Phone 01223 267070
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>
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