On Tue, Jan 28, 2020 at 7:26 AM CASS Philip <[email protected]> wrote:
>
> I have a query about https://docs.ceph.com/docs/master/cephfs/createfs/:
>
>
>
> “The data pool used to create the file system is the “default” data pool and 
> the location for storing all inode backtrace information, used for hard link 
> management and disaster recovery. For this reason, all inodes created in 
> CephFS have at least one object in the default data pool.”
>
>
>
> This does not match my experience (nautilus servers, nautlius FUSE client or 
> Centos 7 kernel client). I have a cephfs with a replicated top-level pool and 
> a directory set to use erasure coding with setfattr, though I also did the 
> same test using the subvolume commands with the same result.  "Ceph df 
> detail" shows no objects used in the top level pool, as shown in 
> https://gist.github.com/pcass-epcc/af24081cf014a66809e801f33bcb535b (also 
> displayed in-line below)

Can you share the output of `ceph fs dump`.

> It would be useful if indeed clients didn’t have to write to the top-level 
> pool, since that would mean we could give different clients permission only 
> to pool-associated subdirectories without giving everyone write access to a 
> pool with data structures shared between all users of the filesystem.

As Greg mentioned, clients don't read/write the backtraces. It's all
done by the MDS. Therefore, the clients don't require access to the
default data pool.

-- 
Patrick Donnelly, Ph.D.
He / Him / His
Senior Software Engineer
Red Hat Sunnyvale, CA
GPG: 19F28A586F808C2402351B93C3301A3E258DD79D
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