Re: ceph fs (meta) data inconsistent

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Hi all,

the problem re-appeared in the following way. After moving the problematic folder out and copying it back, all files showed the correct sizes. Today, we observe that the issue is back in the copy that was fine yesterday:

[user1@host11 h2lib]$ ls -l
total 37198
-rw-rw---- 1 user1 user1    11641 Nov  2 11:32 dll_wrapper.py

[user2@host2 h2lib]# ls -l
total 44
-rw-rw----. 1 user1 user1     0 Nov  2 11:28 dll_wrapper.py

It is correct in the snapshot though:

[user2@host2 h2lib]# cd .snap
[user2@host2 .snap]# ls
_2023-11-02_000611+0100_daily_1
[user2@host2 .snap]# cd _2023-11-02_000611+0100_daily_1/
[user2@host2 _2023-11-02_000611+0100_daily_1]# ls -l
total 37188
-rw-rw----. 1 user1 user1    11641 Nov  1 13:30 dll_wrapper.py

It seems related to the path, bot the inode number. Could the re-appearance of the 0 length have been triggered by taking the snapshot?

We plan to reboot later today the server where the file was written. Until hen we can do diagnostics while the issue is visible. Please let us know what information we can provide.

Best regards,
=================
Frank Schilder
AIT Risø Campus
Bygning 109, rum S14

________________________________________
From: Gregory Farnum <gfarnum@xxxxxxxxxx>
Sent: Wednesday, November 1, 2023 4:57 PM
To: Frank Schilder; Xiubo Li
Cc: ceph-users@xxxxxxx
Subject: Re:  ceph fs (meta) data inconsistent

We have seen issues like this a few times and they have all been kernel client bugs with CephFS’ internal “capability” file locking protocol. I’m not aware of any extant bugs like this in our code base, but kernel patches can take a long and winding path before they end up on deployed systems.

Most likely, if you were to restart some combination of the client which wrote the file and the client(s) reading it, the size would propagate correctly. As long as you’ve synced the data, it’s definitely present in the cluster.

Adding Xiubo, who has worked on these and may have other comments.
-Greg

On Wed, Nov 1, 2023 at 7:16 AM Frank Schilder <frans@xxxxxx<mailto:frans@xxxxxx>> wrote:
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
=======
RANK  STATE     MDS       ACTIVITY     DNS    INOS
 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
STANDBY MDS
  ceph-10
  ceph-08
  ceph-09
  ceph-12
MDS version: ceph version 15.2.17 (8a82819d84cf884bd39c17e3236e0632ac146dc4) octopus (stable)

There is no health issue:

# ceph status
  cluster:
    id:     abc
    health: HEALTH_WARN
            3 pgs not deep-scrubbed in time

  services:
    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:

  data:
    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

  io:
    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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