Most mechanical hard drives have a small hole along with text that reads something like: “DO NOT COVER.” This is the hard drive’s breather hole, which equalizes internal pressure with the outside environment.
Covering this hole can break your hard drive by disrupting its aerodynamics. That’s all you need to know — but if you want more details, we’ll explain the physics below.
If you’ve lost data due to a hard drive failure or for any other reason, we’re here to help. Datarecovery.com provides risk-free evaluations and a comprehensive no data, no charge guarantee: If we’re unable to recover the files you need, there’s no charge for the attempt.
Set up a case online or read on to learn more about how hard drives function.
How the Hard Drive Air Bearing Works
To understand the breather hole, you’ll need a very, very basic understanding of how a hard drive reads data.
Hard drives contain platters, which store data magnetically, and read/write heads, which — you guessed it — read and write the data.The read/write heads do not touch the platters; they fly on a microscopic cushion of air known as an air bearing.
The air bearing is created by the motion of the platters, and the gap between the head and the platter is extraordinarily small (often less than 5 nanometers). For context, a human hair is roughly 75,000 nanometers wide.
Because the heads rely on air density to maintain their lift, the internal pressure of the drive must match the external ambient pressure. If you take a hard drive from sea level to the top of a mountain, the air inside needs to expand and equalize. The breather hole allows this air to pass in and out of the chassis safely.
Hard Drive Internal Breather Filters
A common misconception is that the breather hole is a direct, open tunnel to the platters. If that were true, it would be a terrible design: A single speck of dust could destroy the drive instantly by disrupting the air bearing.
To prevent this, there’s a breather filter to prevent contaminants while allowing air molecules to pass through. It ensures that while pressure is equalized, the environment inside the drive remains a cleanroom-class environment (which is why data recovery firms need cleanrooms to open hard drives).
What Happens If You Cover a Breather Hole?
If you place a sticker over the hole or mount the drive in a bracket that obstructs the airflow, you prevent the drive from equalizing with the ambient pressure. As the drive heats up during operation, the air inside expands; as it cools, the air contracts. Without a functional breather hole, these temperature changes create significant pressure differentials.
That can lead to two failure scenarios:
- High Pressure: The increased pressure can alter the density of the air bearing. That can cause the heads to fly too high, leading to read/write errors. The magnetic field is too weak to reach from the platter to the heads.
- Low Pressure: If the internal pressure drops (for instance, if the drive cools rapidly or is operated at a high altitude without equalization), the air density decreases. The air bearing loses its ability to support the weight of the slider, and the heads fly low. The heads may make physical contact with the platters, causing a head crash. Head crashes may result in permanent data loss, though the extent of the damage will vary.
Never stick a label, warranty sticker, or mounting tape over the small hole on the drive lid. If you are installing a drive into a tight enclosure, ensure there is at least a millimeter of clearance above the hole.
Why Helium Hard Drives Don’t Have Breather Holes
If you look at a modern, high-capacity enterprise drive, you might notice there is no breather hole. These are helium-filled drives.
Because helium is much less dense than air, it creates less turbulence, allowing manufacturers to stack more platters into a standard case. However, helium atoms are so small that they escape through standard seals, so these drives are hermetically sealed (welded shut). They do not need to equalize pressure, so they have no breather holes.
Professional Solutions for Hard Drive Data Recovery
The breather hole is a vital piece of engineering. Respect the “Do Not Cover” warning, particularly if you’re building a PC or server.
Remember, all mechanical drives will eventually fail. When that happens, we’re here here to help. Datarecovery.com operates on-site cleanrooms at every location, and with our industry-leading hardware library, we provide high success rates, fast turnaround times, and comprehensive solutions for all data storage devices.
If your hard drive is making noise or failing to mount, contact us at 1-800-237-4200 or submit a case online for a free evaluation.
