Hi Joel,

All drbd devices are in the same volume group on the same physical disk. The physical disk is a hardware raid-1 device consisting of 2 ssd disk. E.g:
lvdisplay /dev/vg_ssd/test-lv
  --- Logical volume ---
  LV Path                /dev/vg_ssd/test-lv
  LV Name                test-lv
  VG Name                vg_ssd
  LV UUID                HWkc5O-FPBp-hjCb-WHjU-1Z1T-Wb1N-nUtRmH
  LV Write Access        read/write
  LV Creation host, time barentsz, 2019-06-12 09:54:27 +0200
  LV Status              available
  # open                 1
  LV Size                40.00 GiB
  Current LE             10240
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     1024
  Block device           254:16
and:
lvdisplay /dev/vg_ssd/vm_prace-ldap
  --- Logical volume ---
  LV Path                /dev/vg_ssd/vm_prace-ldap
  LV Name                vm_prace-ldap
  VG Name                vg_ssd
  LV UUID                KbAvaa-F9ER-NNfW-tPmb-C4WF-CHXP-ZheJed
  LV Write Access        read/write
  LV Creation host, time barentsz, 2017-11-02 15:33:06 +0100
  LV Status              available
  # open                 2
  LV Size                38.00 GiB
  Current LE             9728
  Segments               2
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     1024
  Block device           254:9

The drbd status on the failing R0 device on this host is:
 0:r0/0  Connected/Connected Secondary/Primary   UpToDate/UpToDate

Regards,
Rob



On 6/12/19 10:39 AM, Joel Colledge wrote:
Hi Rob,

This message indicates that mounting with DAX is failing here:
https://github.com/openSUSE/kernel/blob/SLE12-SP4/drivers/dax/super.c#L131

But DRBD performs the corresponding check here:
https://github.com/LINBIT/drbd-9.0/blob/drbd-9.0.18-1/drbd/drbd_dax_pmem.c#L57

I don't know why the check fails for the DAX mount but succeeds for DRBD. I suggest you set up a DRBD resource using exactly this vg_ssd/test-lv that you used for the mount test. It is possible that the LV you are using for DRBD and the test LV are different in some way, e.g. they have been placed on different backing devices. If DRBD works successfully on this LV then we need to find out what the difference between the LVs is.

Best regards,
Joel


On Wed, Jun 12, 2019 at 10:00 AM Rob van der Wal <[email protected] <mailto:[email protected]>> wrote:

    Hi Joel,

    The additional debug setting gives one additional line:
    2019-06-12T09:58:27.977088+02:00 barentsz kern warning kernel - -
    - [525370.955129] EXT4-fs (dm-16): DAX enabled. Warning:
    EXPERIMENTAL, use at your own risk
    2019-06-12T09:58:27.977121+02:00 barentsz kern debug kernel - - -
    [525370.955135] dm-16: error: dax access failed (-95)
    2019-06-12T09:58:27.977122+02:00 barentsz kern err kernel - - -
    [525370.955136] EXT4-fs (dm-16): DAX unsupported by block device.
    Turning off DAX.
    2019-06-12T09:58:27.977124+02:00 barentsz kern info kernel - - -
    [525370.957006] EXT4-fs (dm-16): mounted filesystem with ordered
    data mode. Opts: dax

    Regards,
    Rob


    On 6/12/19 9:50 AM, Joel Colledge wrote:
    Hi Rob,

    This is strange, since the filesystem DAX access uses essentially
    the same checks as DRBD does. You can get more detail about the
    failure by doing the mount test again after enabling the relevant
    debug logging as follows:
    echo "file drivers/dax/super.c +p" >
    /sys/kernel/debug/dynamic_debug/control

    Perhaps there is a subtle difference in the checks that DRBD does
    which is relevant for your device on this kernel.

    Best regards,
    Joel


    On Wed, Jun 12, 2019 at 8:04 AM Rob van der Wal
    <[email protected] <mailto:[email protected]>> wrote:

        Hi Joel,

        Yes, I can mount with "-o dax":

        lvcreate -L 40G -n test-lv  vg_ssd
          scan_dev_close /dev/sdb2 no DEV_IN_BCACHE set
          Logical volume "test-lv" created.
        mkfs.ext4 -b 4K /dev/vg_ssd/test-lv
        mount -o dax /dev/vg_ssd/test-lv /mnt
        df /mnt
        Filesystem                  1K-blocks  Used Available Use%
        Mounted on
        /dev/mapper/vg_ssd-test--lv  41022688 49176 38859976   1% /mnt

        But it shows a failure in syslog:
        [518270.833954] EXT4-fs (dm-16): DAX enabled. Warning:
        EXPERIMENTAL, use at your own risk
        [518270.833959] EXT4-fs (dm-16): DAX unsupported by block
        device. Turning off DAX.
        [518270.835599] EXT4-fs (dm-16): mounted filesystem with
        ordered data mode. Opts: dax

        Regards,
        Rob


        On 6/11/19 3:57 PM, Joel Colledge wrote:
        Hi Rob,

        This is strange. It seems that your LV is reporting that it supports
        PMEM/DAX. I suggest that you check that this issue also occurs without
        DRBD. For example, create a filesystem and try to mount it with DAX
        enabled:
        mkfs.ext4 -b 4K /dev/<your-lv>
        mount -o dax /dev/<your-lv> <somewhere>

        The check the syslog to see whether DAX was successfully enabled. You
        can see the expected success and failure output here:
        https://nvdimm.wiki.kernel.org/#filesystems

        Best regards,
        Joel

        PS Please "reply all" to keep the mailing list in CC


        On Tue, Jun 11, 2019 at 2:53 PM Rob van der Wal
        <[email protected]>  <mailto:[email protected]>  wrote:
        Hi Joel,

        I've build the module from source (downloaded 
fromhttps://www.linbit.com/en/drbd-community/drbd-download/).

        I think we don't use external metadata and we are using a ssd disk for 
storing. This is a part of our drbd.conf:
        drbd.conf:
             on barentsz {
                 node-id 1;
                 device           /dev/drbd0 minor 0;
                 disk             /dev/vg_ssd/vm_prace-ldap;
                 meta-disk        internal;
                 address          ipv410.0.0.30:7788  <http://10.0.0.30:7788>;
             }


        LVM info:
           PV /dev/sdb2   VG vg_ssd          lvm2 [446.43 GiB / 102.43 GiB free]
           ACTIVE            '/dev/vg_ssd/vm_prace-ldap' [38.00 GiB] inherit

        The requested line in the syslog is:
        [1037978.736262] drbd r0/0 drbd0: meta-data IO uses: dax-pmem

        But I don't think we are using a PMEM device so this looks not correct.

        Regards,
        Rob van der Wal


-- Rob van der Wal
        Supercomputing | SURFsara | Science Park 140 | 1098 XG
        Amsterdam | T +31 20 800  1300 | [email protected]
        <mailto:[email protected]> | www.surfsara.nl
        <http://www.surfsara.nl> |

                    We are ISO 27001 certified and meet the high
        requirements for information security.



-- Joel Colledge - Software Developer
    +43-1-817-82-92 x53 <tel:+4318178292>
    [email protected] <mailto:[email protected]>

    LIN <http://www.linbit.com/en/>BIT <http://www.linbit.com/en/> |
    Keeping the Digital World Running
    DRBD HA - Disaster Recovery - Software-defined Storage
    t <https://twitter.com/linbit> / f
    <https://www.facebook.com/pg/linbitdrbd/posts/> / in
    <https://www.linkedin.com/company/linbit> / y
    <https://www.youtube.com/user/linbit> / g+
    <https://plus.google.com/+Linbit/about>

    DRBD® and LINBIT® are registered trademarks of LINBIT, Austria.

-- Rob van der Wal
    Supercomputing | SURFsara | Science Park 140 | 1098 XG Amsterdam |
    T +31 20 800  1300 | [email protected]
    <mailto:[email protected]> | www.surfsara.nl
    <http://www.surfsara.nl> |

                We are ISO 27001 certified and meet the high
    requirements for information security.



--
Joel Colledge - Software Developer
+43-1-817-82-92 x53 <tel:+4318178292>
[email protected] <mailto:[email protected]>

LIN <http://www.linbit.com/en/>BIT <http://www.linbit.com/en/> | Keeping the Digital World Running
DRBD HA - Disaster Recovery - Software-defined Storage
t <https://twitter.com/linbit> / f <https://www.facebook.com/pg/linbitdrbd/posts/> / in <https://www.linkedin.com/company/linbit> / y <https://www.youtube.com/user/linbit> / g+ <https://plus.google.com/+Linbit/about>

DRBD® and LINBIT® are registered trademarks of LINBIT, Austria.

--
Rob van der Wal
Supercomputing | SURFsara | Science Park 140 | 1098 XG Amsterdam | T +31 20 800  1300 | [email protected] | www.surfsara.nl |

            We are ISO 27001 certified and meet the high requirements for information security.

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