On Tue, Jan 28, 2020 at 7:26 AM CASS Philip <p.cass(a)epcc.ed.ac.uk> 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