Introduction
Hard drive crashes are one of the most frustrating experiences one can have with a computer. The inability to read data off of the hard drive can render a computer useless. Even if the OS can run, the data may be inaccessible or damaged. The only way to recover from such a failure is to typically restore data from a backup onto a new drive with all the software installed from scratch. If no backup is available, then the data is either lost or will cost a lot for recovery services to retrieve.
This article is going to take a look at what causes hard drive failures, if failures are becoming more frequent and what steps one can take to try and avoid problems in the event of a failure.
Hard Drive Basics
Before understanding what can cause a failure, it is important to know the basics of how a hard drive functions. A hard drive is essentially a large device with magnetic storage media that is encased on rigid platters. This allows the drive to store large amounts of data that can be accessed and written to very quickly.
Every hard drive is comprised of several key components: case, drive motor, platters, drive heads and a logic board. The case provides protection for the drive in a sealed environment away from dust particles. The motor spins the drive up so the data can be read off of the platters. The platters hold the magnetic media that stores the actual data. The drive heads are used to read and write the data to the platters. Finally the logic board controls how the drive interfaces and talks to the rest of the computer system.
For a more detailed look at what a hard drive is, I recommend reading the “How Hard Drives Work” from How Stuff Works.
Common Drive Failures
The most common failure for a hard drive is something called a head crash. A head crash is any instance where the drive head manages to touch a platter. When this happens, the magnetic media will be etched off of the platter by the head and render both the data and the drive head inoperable. There is no clean recovery from such a failure.
Another common failure comes from imperfections on the magnetic media. Any time that a sector on the disk fails to properly hold the magnetic alignment will cause data to be inaccessible. Typically drives will have a few of these located on the platter, but they are marked out of use by a low level format from the manufacturer. Later low level formats can be done to mark sectors as unusable so they will not be used, but this is a long process that erases all data from the drive.
Mobile systems tended to be prone to platters that shattered. This was due to the fact that most hard drive platters are made of glass and were susceptible to shock. Most manufacturers have or are switching to other materials to prevent this from happening.
If there is electrical problems with the logic board, data on the drive can become unreadable or damaged. This is due to the logic board being unable to properly communicate between the computer system and the hard drive.
MTBF
In order for consumers to get a good idea of the lifespan of a hard drive, a drive was rated by something called MTBF. This term stands for Mean Time Between Failure and is used to represent the length of time that 50 percent of drives would fail before and 50 percent would fail after. It is used to give an idea to a buyer as to the average amount of time the device will function for. This was typically listed by the manufacturers on all computer drives but in recent years it has been removed from all consumer drives. They are still listed for enterprise class hard drives.
Capacity vs. Reliability
Hard drive sizes have been increasing dramatically over the last few years. This is due to the increase in the density of data being stored on the platters and the number of platters that are being placed inside of a hard drive case. For example, most drives used to feature two or maybe three platters, but many now can have up to four total platters. This increase in the number of parts and the reduction in space has greatly reduced the tolerances that the drives have and increases the amount of possible chance of failure.
