Suppose there was a LV called lv_dbbackup under vg_root which is mounted under /db_backup. But recently for official purpose I created a new VG called vg_backup and by unmounting /db_backup from previously created vg_root-lv_backup i want to use /db_backup to newly created vg_backup-lv_backup. But the problem occurred when i unmounted /db_backup from existing vg_root-lv_backup and try to mount /db_backup with newly created vg_backup-lv_backup. In that case /db_backup is not mounted with newly created vg_backup-lv_backup but when i create another directory for example: /test and try to mount vg_backup-lv_backup with newly created directory(/test or whatever except /db_backup) it works properly.
I'm using ext4 file system and Its a mission critical system so that i'm unable to change /db_backup mount point cause if i change, then it will be a nightmare to Database Team.