Mounted disk does not contain SELinux labels.

After mounting the disk the listed below problem appears.

root# mount -v /dev/sdb1 /mnt/backup
mount: /mnt/backup does not contain SELinux labels.
You just mounted an file system that supports labels which does not
contain labels, onto an SELinux box. It is likely that confined
applications will generate AVC messages and not be allowed access to
this file system. For more details see restorecon(8) and mount(8).
mount: /dev/sdb1 mounted on /mnt/backup.

The SELinux warning is fixed by “restorecon -R /mnt/backup“.