What is SMART?
SMART (Self-Monitoring, Analysis and Reporting Technology) is a monitoring system included in computer hard disk drives (HDDs) and solid-state drives (SSDs) [1]. It was first developed by IBM in 1992. SMART provides the drive’s controller with the ability to monitor, analyze, and report back various indicators of reliability with the goal of anticipating hardware failures.
The purpose of SMART is to detect impending drive failures while there is still time for the user to take preventative action, such as copying data to a replacement drive [2]. SMART works by monitoring different attributes within a drive that are indicative of reliability and performance. These attributes are things like spin retry counts, reallocation event counts, offline reallocation counts, etc. By tracking changes in these metrics over time, SMART attempts to detect degradation and alert the user so action can be taken before failure occurs.
SMART Attributes
SMART monitors a number of attributes related to the health and performance of a hard drive. Some key SMART attributes include:
1. Read Error Rate – Measures the rate of hardware read errors that occurred when reading data from disk. A high rate may indicate a faulty disk head or physical defects on disk platters. (Source)
2. Spin-Up Time – Measures how long it takes for the disk platters to spin up to operating speed on startup. Longer spin-up times can indicate wear on the spindle motor or internal parts. (Source)
3. Power-On Hours – Tracks the total running hours for the drive. Higher values indicate more wear. However, lifespan also depends on operating conditions. (Source)
4. Reallocated Sectors Count – Tallies sectors that have been remapped due to read/write errors. High counts show the drive has had trouble accessing certain areas. (Source)
There are many other SMART attributes that track drive temperatures, seek errors, bad blocks, and performance factors like data transfer speeds. Together, they provide vital insights into the health and reliability of a hard drive.
How SMART Works
SMART works by having the hard drive continually monitor and analyze critical drive attributes related to performance and reliability [1]. The principles behind SMART are:
- The hard drive has sensors that monitor various internal operations and performance factors.
- These sensors generate raw statistical data related to drive reliability.
- The drive firmware analyzes this data to detect trends and possible problems.
There are many attributes that SMART can monitor, but these will vary depending on the drive model and manufacturer [2]. Some common attributes include:
- Read error rate
- Spin-up time
- Reallocated sectors count
- Seek error rate
- Power-on hours
- Temperature
- Unsafe shutdown count
The methods for data collection include [3]:
- Internal performance logs and metrics
- Drive self-tests and diagnostics
- Statistical analysis algorithms
- Error logging
By continuously monitoring these attributes over time, SMART aims to detect evidence of hardware problems before they lead to actual failure.
Using SMART Tools
There are various tools available to monitor SMART data and run self-tests. The operating system often includes basic built-in SMART capabilities.
For example, Windows has the Disk Checking utility that can read SMART attributes and run checks (PassMark). Linux distributions typically include smartctl, a command line tool for querying SMART data. Mac OS also has built-in SMART functionality through Disk Utility.
There are also many third party utilities that offer more advanced SMART monitoring and testing capabilities, such as:
- CrystalDiskInfo (Windows)
- GSmartControl (Linux, Mac OS)
- HD Sentinel (Windows)
- Hard Disk Sentinel (Windows, Linux, DOS)
These tools allow you to view all SMART attributes, interpret their values, run various types of drive tests, and set up alerts or scheduled checks. Some also include drive benchmarking, lifespan predictions, temperature monitoring, and bad sector detection.
To utilize these SMART tools, you would typically download and install the utility, open it, select the drive you want to check, and view the SMART data. Most tools provide an overall drive health status based on attribute thresholds, as well as the option to run manual or scheduled tests. Interpreting specific attribute values may require some research to understand the meaning and acceptable ranges.
SMART Self-Tests
Hard drives and SSDs have the ability to perform self-tests using SMART technology to scan for potential issues. There are two main types of SMART self-tests:
- Offline tests: These are comprehensive tests that scan the entire disk surface area. They put the drive into an offline state so it is not accessible during the test. Offline tests can take several hours to complete.
- Online tests: These are faster, mini-tests that run in the background while the drive is online and accessible. They usually only take a few minutes to run.
Offline tests are more thorough while online tests allow the drive to remain available. Most manufacturers provide tools to run both online and offline SMART self-tests on their drives (see https://www.passmark.com/products/diskcheckup/). On Windows, self-tests can also be scheduled through the Disk Defragmenter utility.
It’s recommended to run regular SMART self-tests to identify any reliability issues early on. Checking SMART attributes after running an offline test can provide deeper insight into the drive’s health. Running self-tests is an important part of monitoring drive health over time.
Interpreting SMART Data
To understand what S.M.A.R.T data means, you need to look at the attribute values and thresholds. Each attribute has a raw value and sometimes a normalized value that ranges from 1 to 253. The normalized value makes it easier to interpret the raw value.
In general, lower values are better. If a value starts approaching or exceeding the threshold (usually between 100-253), that indicates a problem with that attribute. For example, if the read error rate approaches 253, that means the drive is experiencing more read errors than normal.
However, you don’t want to panic if a single attribute exceeds the threshold. Multiple attributes exceeding thresholds over time indicate a drive problem. Some key attributes to watch are read/write error rate, reallocated sectors count, and seek error rate according to this guide. Though every manufacturer uses different thresholds, so checking the drive documentation is recommended.
In summary, keep an eye on any attributes exceeding thresholds or raw values over 100. But don’t be alarmed by an occasional spike, look for patterns over time. Use S.M.A.R.T as an early warning system, not a definitive failure alert.
Using SMART Data
One of the main benefits of SMART is using it for early detection of disk problems before they become catastrophic failures. By monitoring various SMART attributes, drops or increases outside of normal thresholds can indicate issues like bad sectors, mechanical wear, or unstable electronics.
Regularly checking SMART data allows you to monitor the overall health status of a drive and watch for signs of degradation over time. This is useful for scheduling preventative drive replacements before failures occur and cause data loss.
Key SMART attributes to monitor for early warning signs include Reallocated Sectors Count, Seeks Errors, and Spin Retry Count. Sudden increases in these values can indicate physical problems with the platters, heads, or motors.
By keeping an eye on SMART data and replacing drives proactively when their health starts declining, catastrophic in-service failures can be avoided.
Limitations of SMART
While SMART provides valuable insights into the health of a hard drive, it has some important limitations to be aware of:
SMART is not a backup or replacement for backups. While it can help predict failures, SMART data does not protect against data loss. Regular backups are still essential.
SMART focuses on specific mechanical or electronic indicators of drive health, so it does not detect all potential failure modes. Catastrophic failures can still occur without warning from SMART.
SMART stats may also produce false positives – indicating a problem when the drive is actually still reliable. Certain SMART attributes reaching threshold values do not guarantee imminent failure.
Overall, SMART provides useful supplemental information about drive health, but does not make traditional backup and redundancy practices any less important.[1]
[1] “How reliable is HDD SMART data?” Server Fault, 2013. https://serverfault.com/questions/519726/how-reliable-is-hdd-smart-data
SMART for SSDs
SSDs (solid state drives) function differently than traditional HDDs (hard disk drives) and thus have different SMART attributes that require monitoring. Some key differences include:
SSDs do not have mechanical moving parts like HDDs, so attributes related to drive spin-up time, spin retries, etc. do not apply. Important attributes for SSDs include wear leveling, bad blocks, and endurance.
Additional monitoring is needed for SSDs as they have finite write endurance before wearing out, unlike HDDs which can withstand almost unlimited writes. Key stats to monitor include total data written, spare blocks remaining, and percentage lifetime used [1]. SMART tools can track SSD health and estimate remaining lifespan.
Newer SMART standards have added attributes specifically for SSDs. For example, Attribute 231 monitors SSD endurance by tracking the percentage of lifetime writes used. This helps predict when the drive may need replacing.
Future of SMART
SMART technology continues to evolve to meet the needs of modern storage devices. Some emerging capabilities and integrations include:
Enhanced capabilities: Future SMART attributes may monitor additional metrics like partial/weak writes, latency, and temperatures at different sections of the platter to identify problems sooner.1
Integration with AI/ML: Machine learning algorithms can be applied to SMART data to predict failures before traditional thresholds are reached. This allows for more proactive prevention of issues.2
New monitoring methods: As hard drives scale up in capacity, full media scans are becoming less feasible. Methods like zoned failure prediction can target high-risk areas to make monitoring more efficient.3
While SSDs are gaining popularity, HDDs continue advancing in parallel. SMART evolves with new techniques to keep improving failure prediction and ensuring reliability of traditional spinning drives into the future.
