How to Read Your SSD's SMART Data

Your SSD knows when it's dying. It tracks dozens of health metrics internally and makes them available through a system called SMART (Self-Monitoring, Analysis, and Reporting Technology). The problem? SMART data looks like alien hieroglyphics to most people.

Let's decode it together so you can understand exactly what your drive is telling you.

What Is SMART?

SMART is a monitoring system built into nearly every modern storage device - SSDs, HDDs, and NVMe drives. It continuously tracks things like:

How many times the drive has been powered on
Total data written over its lifetime
Number of errors encountered
Temperature history
Remaining lifespan estimation

This data is stored on the drive itself and can be read by software like TagPulse, CrystalDiskInfo, or your drive manufacturer's utility.

SSD vs HDD SMART Data

SSDs and HDDs track different attributes because they work differently. SSDs don't have spinning platters, so they track things like "wear leveling" instead of "spin-up time." This guide focuses on SSD-specific attributes.

The Most Important SMART Attributes

Not all SMART attributes are equally important. Here are the ones that actually matter for predicting drive failure:

Attribute What It Means Concern Level

Percentage Used How much of the drive's rated lifespan has been consumed. At 100%, the drive has exceeded its design specification - it may still work, but reliability decreases. Critical

Media Errors Uncorrectable errors when reading/writing data. Any non-zero value here is concerning - it means data couldn't be read even after error correction. Critical

Reallocated Sectors Number of bad cells that have been replaced with spare cells. Some reallocation is normal; rapid increases indicate accelerating wear. Important

Available Spare Percentage of spare blocks remaining. SSDs reserve extra capacity to replace worn-out cells. Below 10% means the drive is running low on replacements. Important

Temperature Current operating temperature. SSDs throttle performance above 70°C and can be damaged above 85°C. Sustained high temps also accelerate wear. Important

Total Data Written Lifetime writes to the drive. Compare to the TBW (Terabytes Written) rating in your drive's specs. Useful for tracking wear rate. Informational

Power On Hours Total hours the drive has been powered. Useful for warranty claims and understanding usage patterns. Not a direct health indicator. Informational

Understanding "Percentage Used"

This is the single most important number for SSD health. Here's what different values mean:

SSD Health by Percentage Used

0% - Excellent 50% 100% - End of Rated Life

0-25%: Drive is practically new. No concerns.
25-50%: Normal wear for a used drive. Still plenty of life left.
50-75%: Moderate wear. Start planning for replacement in the next year or two.
75-90%: Significant wear. Replacement recommended soon. Ensure backups are current.
90-100%: Critical. Replace immediately. The drive has exceeded its design lifespan.
100%+: Living on borrowed time. The drive is past its rated endurance. Back up NOW.

Important Note

100% doesn't mean the drive will immediately fail - many drives continue working well beyond their rated lifespan. But the manufacturer no longer guarantees reliability, and failure probability increases significantly.

Red Flags to Watch For

Beyond the raw numbers, watch for these warning patterns:

Rapidly Increasing Reallocated Sectors

If reallocated sector count jumped from 5 to 50 in a month, your drive is failing fast. A stable count that slowly grows is normal; sudden spikes are not.

Any Media Errors

This should always be zero. Any non-zero value means uncorrectable errors occurred - data was lost. Even a single media error is a red flag.

Available Spare Dropping Below 10%

Your SSD is running out of backup cells. Once this hits 0%, the drive can't compensate for worn-out cells anymore.

Unsafe Shutdowns Increasing

While not always the drive's fault (could be power issues), frequent unsafe shutdowns can indicate the drive is crashing. Check your power supply too.

How TagPulse Helps

Reading SMART data manually is tedious, and changes happen slowly - you won't notice if a value gradually creeps up over months. TagPulse solves this by:

Continuous monitoring - Checks SMART data automatically in the background
Trend detection - Notices when values are changing faster than normal
Plain English alerts - Instead of "Attribute 05 value 98," you get "Your SSD health has dropped - consider backing up important files"
History tracking - See how your drive's health has changed over time

Pro Tip

Check your SSD's TBW (Terabytes Written) rating in the product specs. Compare it to "Total Data Written" in SMART. If you've written 500TB on a drive rated for 600TBW, you've used about 83% of its rated endurance.

When to Replace Your SSD

Based on SMART data, consider replacement when:

Percentage Used exceeds 80%
Media Errors appear (any non-zero value)
Available Spare drops below 10%
Reallocated sector count is rapidly increasing
You're experiencing unexplained slowdowns or freezes

SSDs don't give much warning before total failure. When SMART data starts looking bad, act quickly - back up your data and plan for replacement.

Monitor Your SSD Health Automatically

TagPulse watches your drive's SMART data 24/7 and alerts you in plain English before problems become disasters.

Download TagPulse Free