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.



--
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