ceph fs (meta) data inconsistent

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Dear fellow cephers,

today we observed a somewhat worrisome inconsistency on our ceph fs. A file created on one host showed up as 0 length on all other hosts:

[user1@host1 h2lib]$ ls -lh
total 37M
-rw-rw---- 1 user1 user1  12K Nov  1 11:59 dll_wrapper.py

[user2@host2 h2lib]# ls -l
total 34
-rw-rw----. 1 user1 user1     0 Nov  1 11:59 dll_wrapper.py

[user1@host1 h2lib]$ cp dll_wrapper.py dll_wrapper.py.test
[user1@host1 h2lib]$ ls -l
total 37199
-rw-rw---- 1 user1 user1    11641 Nov  1 11:59 dll_wrapper.py
-rw-rw---- 1 user1 user1    11641 Nov  1 13:10 dll_wrapper.py.test

[user2@host2 h2lib]# ls -l
total 45
-rw-rw----. 1 user1 user1     0 Nov  1 11:59 dll_wrapper.py
-rw-rw----. 1 user1 user1 11641 Nov  1 13:10 dll_wrapper.py.test

Executing a sync on all these hosts did not help. However, deleting the problematic file and replacing it with a copy seemed to work around the issue. We saw this with ceph kclients of different versions, it seems to be on the MDS side.

How can this happen and how dangerous is it?

ceph fs status (showing ceph version):

# ceph fs status
con-fs2 - 1662 clients
 0    active  ceph-15  Reqs:   14 /s  2307k  2278k  
 1    active  ceph-11  Reqs:  159 /s  4208k  4203k  
 2    active  ceph-17  Reqs:    3 /s  4533k  4501k  
 3    active  ceph-24  Reqs:    3 /s  4593k  4300k  
 4    active  ceph-14  Reqs:    1 /s  4228k  4226k  
 5    active  ceph-13  Reqs:    5 /s  1994k  1782k  
 6    active  ceph-16  Reqs:    8 /s  5022k  4841k  
 7    active  ceph-23  Reqs:    9 /s  4140k  4116k  
        POOL           TYPE     USED  AVAIL  
   con-fs2-meta1     metadata  2177G  7085G  
   con-fs2-meta2       data       0   7085G  
    con-fs2-data       data    1242T  4233T  
con-fs2-data-ec-ssd    data     706G  22.1T  
   con-fs2-data2       data    3409T  3848T  
MDS version: ceph version 15.2.17 (8a82819d84cf884bd39c17e3236e0632ac146dc4) octopus (stable)

There is no health issue:

# ceph status
    id:     abc
    health: HEALTH_WARN
            3 pgs not deep-scrubbed in time
    mon: 5 daemons, quorum ceph-01,ceph-02,ceph-03,ceph-25,ceph-26 (age 9w)
    mgr: ceph-25(active, since 7w), standbys: ceph-26, ceph-01, ceph-03, ceph-02
    mds: con-fs2:8 4 up:standby 8 up:active
    osd: 1284 osds: 1279 up (since 2d), 1279 in (since 5d)
  task status:
    pools:   14 pools, 25065 pgs
    objects: 2.20G objects, 3.9 PiB
    usage:   4.9 PiB used, 8.2 PiB / 13 PiB avail
    pgs:     25039 active+clean
             26    active+clean+scrubbing+deep
    client:   799 MiB/s rd, 55 MiB/s wr, 3.12k op/s rd, 1.82k op/s wr

The inconsistency seems undiagnosed, I couldn't find anything interesting in the cluster log. What should I look for and where?

I moved the folder to another location for diagnosis. Unfortunately, I don't have 2 clients any more showing different numbers, I see a 0 length now everywhere for the moved folder. I'm pretty sure though that the file still is non-zero length.

Thanks for any pointers.
Frank Schilder
AIT Risø Campus
Bygning 109, rum S14
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