Life of Computer Disk Drives

(For Geeks Only)
By Joe Callison
21 December 2018

Hard Disk Drives
For most computers, the first parts that fail are those with moving parts that will have mechanical wear and tear. Hard disk drives are usually the first item to go. Hard disk drives, like most electronic components, often have mean time between failure (MTBF) ratings. These are statistical ratings based on accelerated tests to failure that are useful for comparison, but are not related to real world expected life. On average, about one out of twenty consumer hard drives will fail in the first year and a half due mostly to defects in manufacture. That is the price we pay for demanding cheap consumer products.  
After this initial weeding out period, the random failure rate approaches one out of a hundred per year until they start mechanically wearing out at around the third year. It is during the normal use period before reaching the end of the design life that the annualized failure rate (AFR) that some disk drive manufacturers have started using is based on. Statistics on consumer grade drives running continuously at server farms show that 90% will last at least three years before failing, and 80% will last at least four years. Warranties for consumer drives are typically one to three years in length. Drives in computers that are only on for eight hours a day should last longer than drives in continuous use, but not necessarily three times longer as you might expect. Besides the wear and tear to rotating and moving parts, the number of times the drive motor has to start and spin up to several thousand revolutions per minute will wear out the motor and electronic components. Western Digital says “Turning on the drive a few times per day is considered normal usage and should not pose any problems. If a drive is turned on and off excessively on a daily basis, this could affect the longevity of the hard drive’s components.” Western Digital considers their drives to have a five year component design life with normal use. I recommend that your Windows Power & Sleep settings not put your PC to sleep, which also powers down the hard disk drive, if you use the computer frequently throughout the day and are in the habit of shutting the computer off when you are done using it for the day. Alternatively you could set the PC to sleep at no less than 1 hour to reduce the number of times the hard disk drive is powered up each day.

Solid State Disk Drives
Solid state disk drives have no moving parts to wear out, but the electrical cells used to store data can only be written to by electronically charging them a limited number of times before they become unreliable. The disk drive life is typically rated in either MTBF, which is only useful for comparison, or terabytes written (TBW). In normal office use, between 10 and 35 GB are written in a day. For a disk drive to be designed for say 40 GB per day for 5 years, it would need to be rated for at least 73 TBW. The current designs of most solid state disk drives should result in approximately the same average life span as mechanical hard disk drives or more for average consumer use. Solid state disk drives have also been known to fail prematurely due to defects in manufacture just like hard disk drives do. The warranties for consumer grade solid state disk drives are typically three to five years. There is currently not enough data on actual failure rates for solid state disk drives to compare with hard disk drives.

Disk Drive Monitoring
Whichever type of disk drive is used, it should be obvious that a reliable data back up plan should be in place to prevent data loss that has a high probability of happening during the life of the computer. An additional step you can take is to use disk drive monitoring or diagnostic software tool to keep track of the condition of your disk drive. Most of the disk drive manufacturers have their own tool that you can download and use on their brand only. A free tool I like to use that works with any brand of disk drive is covered in the following article:
It is available in a portable form, so you do not even have to install it on the computer to use it. Just download and extract the zip file and run the exe file from the extracted folder, 32 bit or 64 bit as appropriate for your computer. It works for hard disk drives and solid state drives. Be sure to use the Wikipedia links for help in interpreting the data. The Windows calculator app can be used to convert the hexadecimal data to decimal by going to the menu for the app and switching the calculator type to Programming. Click on Hex, enter the hexadecimal value in the calculator, and the decimal value will be shown next to DEC. If the disk drive is shown to be good but the power on hours for a hard disk drive are over 40,000 or total NAND writes are nearing the TBW rating for a solid state disk drive it would be prudent to think about replacing the disk drive unless you are going to be replacing the computer soon.

Understanding MTBF:
An MTBF of 1.4 million hours, determined in say, six weeks of testing, certainly doesn’t mean we can expect an individual device to operate for 159 years before failing. MTBF is a statistical measure, and as such, it can’t predict anything for a single unit. We can use that MTBF rating more accurately, however, to calculate that if we have 1,000 such devices operating continuously in a factory, we can expect one to fail every 58 days or so, for a total of perhaps 19 failures in three years.

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Posted by Joe Callison

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