# Mount reports wrong volumes when using devicemapper

**URL:** <https://forums.docker.com/t/mount-reports-wrong-volumes-when-using-devicemapper/42578>\
**Category:** General\
**Created:** [December 7, 2017, 6:20pm UTC](https://forums.docker.com/t/mount-reports-wrong-volumes-when-using-devicemapper/42578 "2017-12-07T18:20:41Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![nscheer](https://avatars.discourse-cdn.com/v4/letter/n/82dd89/32.png) [@nscheer](https://forums.docker.com/u/nscheer)\
**Post date:** [December 7, 2017, 6:20pm UTC](https://forums.docker.com/t/mount-reports-wrong-volumes-when-using-devicemapper/42578/1 "2017-12-07T18:20:41Z")

</div>

Hi,

just installed an evaluation version of 17.06.2-ee-6 on a freshly installed OL 7.3 host:

```auto
[ns@dummy ~]$ uname -a
Linux dummy 3.10.0-514.26.2.el7.x86_64 #1 SMP Tue Jul 4 07:15:04 PDT 2017 x86_64 x86_64 x86_64 GNU/Linux

[ns@dummy ~]$ cat /etc/oracle-release
Oracle Linux Server release 7.3

[ns@dummy ~]$ docker info
Containers: 0
 Running: 0
 Paused: 0
 Stopped: 0
Images: 0
Server Version: 17.06.2-ee-6
Storage Driver: devicemapper
 Pool Name: vg01-lv_docker_thinpool
 Pool Blocksize: 524.3kB
 Base Device Size: 10.74GB
 Backing Filesystem: xfs
 Data file:
 Metadata file:
 Data Space Used: 19.92MB
 Data Space Total: 42.95GB
 Data Space Available: 42.93GB
 Metadata Space Used: 389.1kB
 Metadata Space Total: 5.369GB
 Metadata Space Available: 5.368GB
 Thin Pool Minimum Free Space: 4.295GB
 Udev Sync Supported: true
 Deferred Removal Enabled: true
 Deferred Deletion Enabled: false
 Deferred Deleted Device Count: 0
 Library Version: 1.02.135-RHEL7 (2016-11-16)
Logging Driver: json-file
Cgroup Driver: cgroupfs
Plugins:
 Volume: local
 Network: bridge host macvlan null overlay
 Log: awslogs fluentd gcplogs gelf journald json-file logentries splunk syslog
Swarm: inactive
Runtimes: runc
Default Runtime: runc
Init Binary: docker-init
containerd version: 6e23458c129b551d5c9871e5174f6b1b7f6d1170
runc version: 810190ceaa507aa2727d7ae6f4790c76ec150bd2
init version: 949e6fa
Security Options:
 seccomp
  Profile: default
Kernel Version: 3.10.0-514.26.2.el7.x86_64
Operating System: Oracle Linux Server 7.3
OSType: linux
Architecture: x86_64
CPUs: 24
Total Memory: 15.37GiB
Name: dummy
ID: VGIU:U5GG:GEMH:MGJR:4X6Q:X4HV:DL4F:BV6M:JI3B:2IWQ:RZQI:KDBK
Docker Root Dir: /var/lib/docker
Debug Mode (client): false
Debug Mode (server): false
Registry: https://index.docker.io/v1/
Experimental: false
Insecure Registries:
 127.0.0.0/8
Live Restore Enabled: false

```

The system has two volume groups:

```auto
[root@dummy /]# vgdisplay
  --- Volume group ---
  VG Name vg00
  System ID
  Format lvm2
  Metadata Areas 1
  Metadata Sequence No 10
  VG Access read/write
  VG Status resizable
  MAX LV 0
  Cur LV 9
  Open LV 9
  Max PV 0
  Cur PV 1
  Act PV 1
  VG Size 135.62 GiB
  PE Size 4.00 MiB
  Total PE 34719
  Alloc PE / Size 13824 / 54.00 GiB
  Free PE / Size 20895 / 81.62 GiB
  VG UUID vuaDZe-puSm-OI15-Nez4-lPT5-ycZp-tPHWex

  --- Volume group ---
  VG Name vg01
  System ID
  Format lvm2
  Metadata Areas 2
  Metadata Sequence No 35
  VG Access read/write
  VG Status resizable
  MAX LV 0
  Cur LV 7
  Open LV 5
  Max PV 0
  Cur PV 2
  Act PV 2
  VG Size 557.73 GiB
  PE Size 4.00 MiB
  Total PE 142780
  Alloc PE / Size 122112 / 477.00 GiB
  Free PE / Size 20668 / 80.73 GiB
  VG UUID TkLgEy-UACf-q2bG-hTEQ-Dep1-vXIl-I3LLC8

```

Here’s what I did to create the docker thinpool:

- `lvcreate --wipesignatures y -n lv_docker_thinpool vg01 -L 40G`
- `lvcreate --wipesignatures y -n lv_docker_thinpoolmeta vg01 -L 5G`
- `lvconvert -y --zero n -c 512K --thinpool vg01/lv_docker_thinpool --poolmetadata vg01/lv_docker_thinpoolmeta`
- `lvchange --metadataprofile docker-thinpool vg01/lv_docker-thinpool`
- `lvs -o+seg_monitor`

Here the daemon.json:

```auto
{
        "storage-driver": "devicemapper",
        "storage-opts":
        [
                "dm.thinpooldev=/dev/mapper/vg01-lv_docker_thinpool",
                "dm.use_deferred_removal=true"
        ]
}

```

Docker-Engine is able to start without any problems.

As per the documentation (c.f. [https://docs.docker.com/engine/userguide/storagedriver/device-mapper-driver/#how-the-devicemapper-storage-driver-works](https://docs.docker.com/engine/userguide/storagedriver/device-mapper-driver/#how-the-devicemapper-storage-driver-works)) I should be able to see the mounted thinpool when docker engine is running, e.g.:

```auto
$ mount |grep devicemapper
/dev/xvda1 on /var/lib/docker/devicemapper type xfs (rw,relatime,seclabel,attr2,inode64,noquota)

```

But here’s what happens on my system:

```auto
[root@dummy/]# mount | grep docker
/dev/mapper/vg00-lv_var on /var/lib/docker/plugins type ext4 (rw,relatime,data=ordered)
/dev/mapper/vg00-lv_var on /var/lib/docker/devicemapper type ext4 (rw,relatime,data=ordered)

```

That is the wrong volume group and the wrong logical volume as well…  
Furthermore, `docker info` reports that the backing filesystem is xfs, not ext4.  
Since everything is running “fine”, I expect this to be just a display problem - but where should I start debugging?

Here is an excerpt of the other lvs that exist on the machine:

```auto
[root@dummy /]# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 136.1G 0 disk
├─sda1 8:1 0 512M 0 part /boot
└─sda2 8:2 0 135.6G 0 part
  ├─vg00-lv_root 253:0 0 2G 0 lvm /
  ├─vg00-lv_swap 253:1 0 16G 0 lvm [SWAP]
  ├─vg00-lv_usr 253:2 0 6G 0 lvm /usr
  ├─vg00-lv_home 253:5 0 2G 0 lvm /home
  ├─vg00-lv_var 253:6 0 16G 0 lvm /var
  ├─vg00-lv_tmp 253:7 0 3G 0 lvm /tmp
  └─vg00-lv_opt 253:8 0 4G 0 lvm /opt
sdb 8:16 0 278.9G 0 disk
└─sdb1 8:17 0 278.9G 0 part
  └─vg01-lv_app 253:9 0 300G 0 lvm /app
sdc 8:32 0 278.9G 0 disk
└─sdc1 8:33 0 278.9G 0 part
  ├─vg01-lv_app 253:9 0 300G 0 lvm /app
  ├─vg01-lv_docker_thinpool_tmeta 253:15 0 5G 0 lvm
  │ └─vg01-lv_docker_thinpool 253:17 0 40G 0 lvm
  └─vg01-lv_docker_thinpool_tdata 253:16 0 40G 0 lvm
    └─vg01-lv_docker_thinpool 253:17 0 40G 0 lvm
sr0 11:0 1 1024M 0 rom

```

So the mount suggests that `/var/lib/docker/plugins` and `/var/lib/docker/devicemapper` are a mount of the same (wrong) logical volume.  
That is, of course, not true:

```auto
[root@dummy/]# ls -l /var/lib/docker/plugins
total 12
drwx------ 4 root root 4096 Dec 7 18:26 b7ee60877053565a5d5807ec497a49bd4f2195860d4c4f25d7049bd54fe4b647
drwx------ 3 root root 4096 Dec 7 16:21 storage
drwx------ 2 root root 4096 Dec 7 16:38 tmp
[root@dummy/]# ls -l /var/lib/docker/devicemapper
total 8
drwx------ 2 root root 4096 Dec 7 18:26 metadata
drwxr-xr-x 2 root root 4096 Dec 7 17:17 mnt

```

Any insight is very appreciated…

Greetings

Nico