What causes hard disk failures

If you are looking for standard procedures and reliable methods, you could read the Guidelines for Media Sanitization (PDF) of the National Institute of Standards and Technology.

For any given medium, there are three basic methods:

• Clear
• Purge
• Physical Destruction

For hard drives they recommend:

Clear:

Overwrite media by using agency-approved and validated overwriting technologies/methods/tools.

Physical Destruction:

• Disintegrate
• Shred
• Pulverize
• Incinerate: incinerate hard disk drives by burning the hard disk drives in a licensed incinerator.

Purge:

1. Purge using Secure Erase. The Secure Erase software can be downloaded from the University of California, San Diego (UCSD) CMRR site.
2. Purge hard disk drives by either purging the hard disk drive in an NSA/CSS-approved automatic degausser or by disassembling the hard disk drive and purging the enclosed platters with an NSA/CSS-approved degaussing wand.
3. Purge media by using agency-approved and validated purge technologies/tools.

Recommendations for flash media (SSDs) are similar, except that degaussing solid state drives is not a viable way to purge them as the data is not stored on magnetic platters.

You can get a pretty good measure of this using the iostat tool.

% iostat -dx /dev/sda 5

Device:         rrqm/s   wrqm/s     r/s     w/s   rsec/s   wsec/s avgrq-sz avgqu-sz   await  svctm  %util
sda               0.78    11.03    1.19    2.82    72.98   111.07    45.80     0.13   32.78   1.60   0.64

The disk utilisation is listed in the last column. This is defined as

Percentage of CPU time during which I/O requests were issued to the device (band-width utilization for the device). Device saturation occurs when this value is close to 100%.