Self-Monitoring, Analysis and Reporting Technology, often abbreviated as S.M.A.R.T., is a hardware monitoring tool that is designed to detect early warning signs of hard drive failure so the user can take the necessary action to prevent data loss or corruption. Compatible with both hard disk drives (HDDs) and some solid-state drives (SSDs), S.M.A.R.T. has saved countless files and untold amounts of data over the years.

The Evolution of S.M.A.R.T.
Like most other forms of technology, S.M.A.R.T. has undergone many changes since its original inception. The earliest version of S.M.A.R.T. didn't provide much more than basic drive failure prediction, which it achieved by monitoring the activities of online and active drives.

The next version included substantial improvements to the failure prediction functionality of S.M.A.R.T. One of the ways it achieved this was through the implementation of automated, offline read scans. It also adds failure prevention via sector error detection and repair.

Finally, the most recent version of S.M.A.R.T. adds on top of the previous iterations by testing all drive sectors - and the data therein - to verify drive and data health.

How Does S.M.A.R.T. Work?
At the most basic level, S.M.A.R.T. works by scanning and monitoring the health of your hard drives. Generally speaking, modern hard drive failures are lumped into one of two categories:

• Predictable: These failures include mechanical wear and the degradation of data storage surfaces. According to some studies, mechanical failures comprise approximately 60% of all hard drive failures in consumer systems.
• Unpredictable: Failures that cannot be reasonably predicted fall into this category. These failures often stem from hardware misuse.

The S.M.A.R.T. protocol focuses on predictable failures, which are automatically documented and tracked. Your status can be checked in a number of ways, but most drive manufacturers offer proprietary utilities that let you view any current failures.

If you are specifically concerned about a drive's S.M.A.R.T. status, you can also run a S.M.A.R.T. test. However, this test does require specialized software.

Common S.M.A.R.T. Warning Signs
However, S.M.A.R.T. ultimately tracks approximately 50 different attributes related to your drive's health. Since some of them are more important than others, it's crucial that you know which ones can be ignored and which ones require immediate action.

• Reallocated Sector Counts: This attribute tracks how many times a damaged drive sector has been reallocated or remapped. It's generally an indicator of excessive wear and tear in both HDDs and SSDs.
• Current Pending Sector Counts: This attribute tracks the overall number of unstable or damaged sectors that have yet to be remapped. Again, this can be indicative of excessive wear.

Some attributes are more relevant to SSDs rather than HDDs. These include:

• Erase Fail Count: This attribute tracks the number of deletion attempts that have failed. It's usually indicative of an SSD that is failing.
• Wear Leveling Count: This attribute provides an estimation of the overall health of your drive. Higher numbers mean a greater amount of wear and tear on your drive.

While some of S.M.A.R.T.'s results have been criticized in the past, and it's accuracy has been question by some data scientists, it's still an effective means of predicting drive failures - even if it's not perfect.

You may read more about S.M.A.R.T. in Wikipedia: Self-Monitoring, Analysis and Reporting Technology.