The /etc/fstab entry uses /dev/vg_data/lv_web, which is a device mapper path. If the logical volume is not activated before the mount, it may not be available. However, the most common issue is that the filesystem is mounted but the content is missing because the mount point is overlaid by another filesystem or the content is on a different logical volume.
Actually, the exhibit shows a fresh filesystem with no data. If after reboot it's empty, it means the filesystem is mounted correctly but the data is not persistent? Wait, the filesystem was just created, so it's empty. The question might be that the administrator expected data to be there? Let me adjust: The exhibit shows creating and mounting, then fstab entry.
After reboot, the directory is empty. The most likely cause is that the logical volume is not activated at boot because the volume group is not automatically activated. In Red Hat, by default, volume groups are activated at boot.
But if the VG is on a remote storage or if there is a delay, it might not be available. However, a common issue is that the fstab entry uses the device mapper path but the system may use different names. Actually, the correct answer is that the filesystem is not mounted at boot because the mount point is not created? No, /var/www/html exists.
Another possibility: the fstab entry uses the device path but the device is not available at the time of mounting. The most likely cause is that the logical volume is not activated before the mount. In systemd, there is a dependency.
But perhaps the simpler answer is that the filesystem type is ext4 but the kernel module is not loaded? Unlikely. Let me think of a typical EX200 scenario: After creating a filesystem and adding to fstab, the system may not mount it at boot if the mount point is used by another filesystem or if there is a UUID conflict. However, the exhibit uses device path, not UUID.
The issue might be that the mount point /var/www/html is a directory that already contains files from a previous mount? But the filesystem is new, so empty. After reboot, the directory is empty because the new filesystem is mounted, but the old data (if any) is hidden. But the question says "the directory is empty", implying it should have data.
Perhaps the administrator expected data from a previous filesystem? The exhibit only shows creation of a new filesystem. So the most likely cause is that the filesystem was created but no data was copied. That seems too trivial.
Let me change the stem: After reboot, the mount fails and the directory is empty. The most likely cause is that the logical volume is not activated. But the exhibit shows the mount command worked.
After reboot, if the LV is not activated, the mount fails, and the directory would be empty (since it's a regular directory). So the correct answer is that the volume group is not auto-activated. However, in Red Hat, by default, volume groups are activated.
To make it not activate, you would set auto_activation_volume_list. But that's advanced. Perhaps the answer is that the fstab entry uses the wrong device path because the LV name changed? LVM names are persistent.
Another common issue: the fstab entry uses /dev/vg_data/lv_web but the system may use /dev/mapper/vg_data-lv_web. Both are acceptable. I think the most plausible is that the volume group is not activated at boot.
Let me craft options accordingly.