Device /dev/sdb excluded by a filter Ubuntu 18.04.02 Server Edition (just installed Ubuntu)

In the PC with two disks I just installed Ubuntu 18.04.02 Server Edition in one of them.

marco@pc:$ sudo pvdisplay
-- Physical volume ---
PV Name       /dev/sda3
VG Name       ubuntu-vg
PV Size       231.38 GiB / not usable
Allocatable   yes
PE Size       4.00 MiB
Total PE      59234
Free PE       58210
Allocated PE  1024
PV UUID       zJfww8-S8hN-iqio-TO88-USuG-IEJF-06in3H

marco@pc:$ sudo fdisk -l
Disk /dev/loop0: 91 MiB, 95308128 bytes, 186344 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/I size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/sda: 232,9 GiB, 250059350016 bytes, 488397168 sectors
Units: sectors of 1 * 512  = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 byte
Disklabel type: gpt
Disk identifier: EE7F5194-52B9-4FFc-A272-30021FAC12C3

Device         Start       End       Sectors     Size    Type
/dev/sda1        2048   1050623      1048576     512M   EFI System
/dev/sda2    1050624    3147775      2097152     1G     Linux filesystem
/dev/sda3    3147776    488394751    485246976  231.4G  Linux filesystem

Disk /dev/sdb: 232.9 GiB, 250059250016 bytes, 488397168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size(logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier:DF99B63F-9A69-46EC-9BA8-47FD4CE8213C

Device         Start       End       Sectors     Size    Type
/dev/sdb1      2048      1050623    1048576      512M    EFI System
/dev/sdb2   1050624      488394751  487344128   232.4G   Linux filesystem

Disk /dev/mapper/ubuntu--vg-ubuntu--lv: 4 GiB, 4294967296 bytes, 8388608 
 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

I want to extend the system to the second SSD:

marco@pc:$ sudo vgextend ubuntu_vg /dev/sdb
  Device /dev/sdb excluded by a filter

Trying to extend the system to just a partition of the second disk:

marco@pc:$ sudo vgextend ubuntu_vg /dev/sdb1
  Can't open /dev/sdb1 exclusively. Mounted filesystem?

in /etc/lvm/lvm.conf I din't find any uncommented filter = or global filter = lines.

What to do in order to disable this "filter" which I did not inserted during the Ubuntu 18.04.02 Server Edition installation process? Looking forward to your kind help. Marco

I SOLVED the problem in this way:

after re-installing Ubuntu 18.04.02 Server Edition in one disk, in order to have a clean situation, I made the following steps:

1) Marked the second disk as "lvm"-disk:

marco@pc:$ sudo pvcreate /dev/sdb
Physical volume "/dev/sdb" successfully created.

2) Extended the volume group to the second disk:

marco@pc:$ sudo vgextend pc-vg /dev/sdb
Volume group "pc-vg" successfully extended

3) Extended the size :

sudo lvextend /dev/mapper/pc--vg-root  -L +240G

4) Resized accordingly the filesystem:

sudo resize2fs /dev/mapper/pc--vg-root