We have a three node setup with ips 172.18.255.21, 172.18.255.22, and 172.18.255.23. Each of the nodes has a mountpoint to an external storage.
mount.cifs //172.18.255.80/share_vertica/ /mnt/share -o username=admin

When I use the following configuration from node1 (172.18.255.21) all works well.

1)
[Mapping]
v_pm_node0001 = 172.18.255.21:/mnt/share/backup_pm1/
v_pm_node0002 = 172.18.255.21:/mnt/share/backup_pm1/
v_pm_node0003 = 172.18.255.21:/mnt/share/backup_pm1/

However when I do the following if tails
2)
[Mapping]
v_pm_node0001 = 172.18.255.21:/mnt/share/backup_pm1/
v_pm_node0002 = 172.18.255.22:/mnt/share/backup_pm1/
v_pm_node0003 = 172.18.255.23:/mnt/share/backup_pm1/

It fails with the following error
[vertica@dal_server1 FROM LSN SETUP]$ /opt/vertica/bin/vbr.py -t backup -c backup_pm.ini
Error: Unable to lock backup location: [Errno 13] Permission denied. Hint: You must have permission to backup locations and the filesystems must support POSIX file locking.
Backup FAILED.

If I do the following that does not use the mounted directory, but only the local disk it works as well even with the IP Mapping that did not work in case #2.
3)
[Mapping]
v_pm_node0001 = 172.18.255.21:/tmp/backup_pm1/
v_pm_node0002 = 172.18.255.22:/tmp/backup_pm1/
v_pm_node0003 = 172.18.255.23:/tmp/backup_pm1/

The following are the vbr log files from the 3 nodes
log from 172.18.255.21
2019/10/10 16:41:16 [461993] 172.18.255.21 is not a known address for "dal_server1": spoofed address?
2019/10/10 16:41:16 [461993] connect from UNKNOWN (172.18.255.21)
2019/10/10 16:41:16 [461993] rsync: connection unexpectedly closed (0 bytes received so far) [Receiver]
2019/10/10 16:41:16 [461993] rsync error: error in rsync protocol data stream (code 12) at io.c(601) [Receiver=3.0.7]
2019/10/10 16:41:17 [462079] 172.18.255.21 is not a known address for "dal_server1": spoofed address?
2019/10/10 16:41:17 [462079] connect from UNKNOWN (172.18.255.21)
2019/10/10 16:41:17 [462079] rsync on vbr/mnt/share/backup_pm1/backup_manifest from UNKNOWN (172.18.255.21)
2019/10/10 16:41:17 [462079] building file list
2019/10/10 16:41:17 [462079] sent 78 bytes received 26 bytes total size 2861

log from 172.18.255.22
2019/10/10 16:41:17 [432209] name lookup failed for 172.18.255.21: Name or service not known
2019/10/10 16:41:17 [432209] connect from UNKNOWN (172.18.255.21)
2019/10/10 16:41:17 [432209] rsync: connection unexpectedly closed (0 bytes received so far) [Receiver]
2019/10/10 16:41:17 [432209] rsync error: error in rsync protocol data stream (code 12) at io.c(601) [Receiver=3.0.7]
2019/10/10 16:41:17 [432259] name lookup failed for 172.18.255.21: Name or service not known
2019/10/10 16:41:17 [432259] connect from UNKNOWN (172.18.255.21)
2019/10/10 16:41:17 [432259] rsync on vbr/mnt/share/backup_pm1/backup_manifest from UNKNOWN (172.18.255.21)
2019/10/10 16:41:17 [432259] building file list
2019/10/10 16:41:17 [432259] sent 78 bytes received 26 bytes total size 2861

log from 172.18.255.23
2019/10/10 16:41:17 [157393] name lookup failed for 172.18.255.21: Name or service not known
2019/10/10 16:41:17 [157393] connect from UNKNOWN (172.18.255.21)
2019/10/10 16:41:17 [157393] rsync: connection unexpectedly closed (0 bytes received so far) [Receiver]
2019/10/10 16:41:17 [157393] rsync error: error in rsync protocol data stream (code 12) at io.c(601) [Receiver=3.0.7]
2019/10/10 16:41:18 [157449] name lookup failed for 172.18.255.21: Name or service not known
2019/10/10 16:41:18 [157449] connect from UNKNOWN (172.18.255.21)
2019/10/10 16:41:18 [157449] rsync on vbr/mnt/share/backup_pm1/backup_manifest from UNKNOWN (172.18.255.21)
2019/10/10 16:41:18 [157449] building file list
2019/10/10 16:41:18 [157449] sent 78 bytes received 26 bytes total size 2861