On Tue, Jan 28, 2020 at 4:26 PM CASS Philip <p.cass@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)

Hmm I think this is tripping over the longstanding issue that omap data is not reflected in the pool stats (although I would expect it to still show up as objects, but perhaps the "ceph df" view has a different reporting chain? Or else I'm confused somehow.)
But anyway...


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.

*Clients* don't need write permission to the default data pool unless you want them to write files there. The backtraces are maintained by the MDS. :)


[root@hdr-admon01 ec]# ceph df detail; ceph fs ls; ceph fs status


    CLASS     SIZE        AVAIL       USED        RAW USED     %RAW USED

    hdd       3.3 PiB     3.3 PiB      32 TiB       32 TiB          0.95

    nvme      2.9 TiB     2.9 TiB     504 MiB      2.5 GiB          0.08

    TOTAL     3.3 PiB     3.3 PiB      32 TiB       32 TiB          0.95



    POOL                           ID     STORED      OBJECTS     USED        %USED     MAX AVAIL     QUOTA OBJECTS     QUOTA BYTES     DIRTY     USED COMPR     UNDER COMPR

    cephfs.fs1.metadata             5     162 MiB          63     324 MiB      0.01       1.4 TiB     N/A               N/A                63            0 B             0 B

    cephfs.fs1-replicated.data      6         0 B           0         0 B         0       1.0 PiB     N/A               N/A                 0            0 B             0 B

    cephfs.fs1-ec.data              7     8.0 GiB       2.05k      11 GiB         0       2.4 PiB     N/A               N/A             2.05k            0 B             0 B

name: fs1, metadata pool: cephfs.fs1.metadata, data pools: [cephfs.fs1-replicated.data cephfs.fs1-ec.data ]

fs1 - 4 clients



| Rank | State  |    MDS     |    Activity   |  dns  |  inos |


|  0   | active | hdr-meta02 | Reqs:    0 /s |   29  |   16  |



|            Pool            |   type   |  used | avail |


|    cephfs.fs1.metadata     | metadata |  324M | 1414G |

| cephfs.fs1-replicated.data |   data   |    0  | 1063T |

|     cephfs.fs1-ec.data     |   data   | 11.4G | 2505T |



| Standby MDS |


|  hdr-meta01 |


MDS version: ceph version 14.2.5 (ad5bd132e1492173c85fda2cc863152730b16a92) nautilus (stable)


[root@hdr-admon01 ec]# ll /test-fs/ec/

total 12582912

-rw-r--r--. 1 root root 4294967296 Jan 27 22:26 new-file

-rw-r--r--. 2 root root 4294967296 Jan 28 14:06 new-file2

-rw-r--r--. 2 root root 4294967296 Jan 28 14:06 new-file-same-inode-as-newfile2


Philip Cass

HPC Systems Specialist – Senior Systems Administrator


Advanced Computing Facility

Bush Estate



Tel:                                        +44 (0)131 4457815

Email:                                   p.cass@epcc.ed.ac.uk 



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