Without DM Multipath, each path from a server node to a storage controller is treated by the system as a separate device, even when the I/O path connects the same server node to the same storage controller. DM Multipath provides a way of organizing the I/O paths logically, by creating a single multipath device on top of the underlying devices.

When using Device Mapper Multipath or other multipath software such as EMC PowerPath or Hitachi Dynamic Link Manager (HDLM), each path to a particular logical unit number (LUN) is registered as a different SCSI device, such as /dev/sdb or /dev/sdc. Display messages

# vgscan 
  WARNING: Not using device /dev/sdb3 for PV eKWtzc-CvWO-3qqf-dwR2-VnlH-pz7u-2uYKWk.
  WARNING: PV eKWtzc-CvWO-3qqf-dwR2-VnlH-pz7u-2uYKWk prefers device /dev/sda3 because device is used by LV.
  Found volume group "ubuntu-vg" using metadata type lvm2

• The two devices displayed in the output are both single paths to the same device
• The two devices displayed in the output are both multipath maps

Solution

Before update filter in /etc/lvm/lvm.conf. The Output command pvscan is :

$ sudo pvscan 
  WARNING: Not using device /dev/sdb3 for PV eKWtzc-CvWO-3qqf-dwR2-VnlH-pz7u-2uYKWk.
  WARNING: PV eKWtzc-CvWO-3qqf-dwR2-VnlH-pz7u-2uYKWk prefers device /dev/sda3 because device is used by LV.
  PV /dev/sda3   VG ubuntu-vg       lvm2 [<928.46 GiB / <828.46 GiB free]
  Total: 1 [<928.46 GiB] / in use: 1 [<928.46 GiB] / in no VG: 0 [0   ]
$

To prevent this warning from appearing, you can configure a filter in the /etc/lvm/lvm.conf file to restrict the devices that LVM will search for metadata.

# This filter accepts the third partition on the first hard drive, while rejecting everything else. 
filter = [ "a|/dev/sda3$|", "r|.*|" ]

After updating /etc/lvm.conf, it’s necessary to update the initrd so that this file will be copied there, where the filter matters the most – during boot.

sudo update-initramfs -u -k all

After update filter in /etc/lvm/lvm.conf

 $ sudo pvscan 
  PV /dev/sda3   VG ubuntu-vg       lvm2 [<928.46 GiB / <828.46 GiB free]
  Total: 1 [<928.46 GiB] / in use: 1 [<928.46 GiB] / in no VG: 0 [0   ]

Reference

• Duplicate PV Warnings for Multipathed Devices