“General failure reading disk”. Who is General Failure, and why is he reading your disk? An old IT joke arising from a critical boot-up error message, but one that illustrates that a common point of failure in computers is the hard disk. Hard disk and power-supply are the most likely components to break down in a computer simply because they contain moving parts that have to keep moving, reliably and consistently, for years and years.
Last week's column covered the need to keep an eye on the power-supply, and specifically to ensure that its fan continues to operate and its vents are kept clear of dust and debris. The hard disk is another matter – it is an internal closed unit roughly the size of a DVD case for desktop computers, or the size of a pair of matchboxes for laptops. Inside is a magnetic disk that spins very fast, with a tiny moving head that reads and writes data on the disk surface. Very clever things have been done to increase the speed and storage capacity of disks even as the reliability and quality of construction have improved. It is now easy to buy half a terabyte of disk space – 500 gigabytes, or 500,000 megabytes. That's a lot of space.
Years ago, a special procedure had to be followed to “park” the moving head inside the hard disk before attempting to move it. If this was not done, there was a significant risk of scratching the surface of the disk with the head – not only making the scratched area unusable, but even worse possibly causing loose fragments that go on to repeatedly get stuck between disk and head causing yet more scratches. Parking is no longer necessary, but all the same, a good knock while the hard disk is operating may well cause problems.
Some disks are available with advanced G-shock protection, ie. they can detect incredibly quickly that they are being kicked, dropped, punched or otherwise abused by the computer user, and they automatically prepare for the resulting G-force. However, most disks need to be treated relatively gently while in use.
The hard disk's other enemy is heat. Disks can do a lot of work at times (watch the disk activity light to get an idea), and while they do, all the physical movement of disk and head causes the release of heat which needs to escape somewhere. On hot days such as we are having in Vanuatu at the moment, that may be enough for the disk to become too hot to touch, risking damage to the disk's internal electronics. Point a fan at the computer if this happens, the extra breeze will be a big help.
Disk hardware and some operating systems provide tools to automatically cope with “bad sectors”, or areas of disk that become unusable for some reason. Some disks have technology that is supposed to warn that a disk is about to fail so that you can take steps to move to another one. Generally speaking, if you see error messages or statistical counters indicating bad sectors, you will need to make sure your backups are up-to-date and working and keep an eye on the disk. If you see more bad sectors appearing over time, you should replace the disk. It is not worth repairing, these are throwaway sealed units.
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