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Operations Guides

NVMe Percentage Used at or above 100%: rated endurance consumed

The NVMe SMART/Health Information Log (Log Page 02h) includes a field called Percentage Used that estimates how much of a drive’s rated write endurance has been consumed. At 100%, the drive has used up its warranted Total Bytes Written (TBW). Above 100%, it is operating beyond its manufacturer endurance rating.

This is not a failure signal. The NVMe specification explicitly allows values up to 255%, and drives routinely continue working past their rated endurance. A drive reporting 150% Percentage Used with 90% Available Spare and zero Media Errors is likely fine. Percentage Used is a planning signal: it tells you where the drive is in its endurance lifecycle so you can sequence replacement before the actual failure indicators (Available Spare exhaustion and Media Errors) force an emergency.

What Percentage Used actually measures

Percentage Used is a vendor-calculated estimate at byte 5 of the SMART/Health Information Log. The NVMe Base Specification defines it as “a vendor specific estimate of the percentage of NVM subsystem life used based on the actual usage and the manufacturer’s prediction of NVM life.”

Key properties:

Range: 0 to 255%. Single byte. Values greater than 254 are clamped to 255.
Basis: Actual NAND writes (program/erase cycles consumed), not raw host writes. The controller factors in wear leveling and garbage collection.
Vendor interpretation: Each vendor calculates the estimate using its own lifetime model. The same workload can produce different trajectories on different drive models.
Update cadence: The NVMe Base Specification requires an update once per power-on hour when the controller is not in a sleep state.

The specification is explicit that a value of 100 “may not indicate an NVM subsystem failure.” The field tracks wear, not health verdict.

Why drives keep working past 100%

The TBW rating is a warranty figure, not a cliff edge. It represents the data volume the manufacturer guarantees can be written under specified workload conditions while maintaining data integrity. Most drives significantly exceed their rated TBW before experiencing hardware failure.

When Percentage Used exceeds 100%:

The warranty endurance has been consumed. The manufacturer’s data integrity guarantee no longer applies.
The drive is not necessarily failing. It still has spare blocks, and its error correction is still functioning.
The drive may continue operating for months or years, but the probability of block failures increases as more cells approach their program/erase cycle limits.

The transition from “past rated endurance but functional” to “actively failing” is signaled by Available Spare declining and Media Errors appearing. Percentage Used tells you the drive is in the risk window; those signals tell you the risk has materialized.

The three signals to read together

Percentage Used is one of three NVMe health metrics that form a complete endurance picture. Reading any one in isolation leads to wrong decisions.

Signal	What it measures	Direction	Failure indicator?
Percentage Used	Estimated endurance consumed (0-255%)	Increases only	No: planning signal
Available Spare	Remaining spare NAND for bad block replacement (0-100%)	Decreases only	Yes: at or below vendor threshold
Media and Data Integrity Errors	Count of uncorrectable data integrity failures	Increases only	Yes: any growth is active data loss

Available Spare and Percentage Used are independent measurements. A drive can show 123% Percentage Used with 100% Available Spare. This is normal. Available Spare tracks remaining spare blocks; Percentage Used tracks estimated endurance consumed. They do not move in lockstep.

Conversely, a drive can show 50% Percentage Used but only 5% Available Spare. This suggests manufacturing defects or unusual wear patterns consuming spare capacity faster than normal endurance depletion would predict. The low Available Spare, not the moderate Percentage Used, is the concern.

flowchart TD
    A["Percentage Used > 100%
Rated endurance consumed"] --> B["Available Spare declining
Spare blocks consumed"]
    B --> C["Media Errors appearing
Active data loss"]
    C --> D["Critical Warning bit 2 or 3 set
Reliability degraded or read-only"]
    D --> E["Drive failure confirmed"]

Percentage Used at or above 100% is the leftmost node: the earliest signal, but it predicts risk, not failure. The cascade progresses through Available Spare depletion and Media Errors before the drive sets Critical Warning bits. Monitoring all three stages gives lead time measured in weeks or months, not hours.

Write amplification: why it climbs faster than you expect

Percentage Used is based on actual NAND program/erase cycles, not host write volume. Write amplification (the ratio of NAND writes to host writes) is always >= 1. The controller generates additional writes through:

Garbage collection: Reclaiming invalidated NAND pages requires reading valid data and rewriting it.
Wear leveling: Distributing writes evenly across all cells means data is periodically moved behind the scenes.
Metadata updates: The flash translation layer mapping table is updated on every write and persisted to NAND.

On a drive with a write amplification factor of 4, every 1 TB of host writes consumes the endurance of 4 TB of NAND writes. Percentage Used climbs four times faster than Data Units Written alone would suggest.

Factors that increase write amplification:

Random small writes (database OLTP workloads, many small files)
Nearly full drives (less free space for efficient garbage collection)
TRIM not reaching the drive (some RAID controllers strip TRIM commands)
Misaligned partitions (each write touches an extra erase block)
Incompressible data on drives with compression (encrypted volumes, pre-compressed data)

You cannot read the write amplification factor directly from the NVMe SMART log. Infer it by comparing Data Units Written (host writes) against the rate of Percentage Used increase relative to the drive’s rated TBW. If the drive is wearing out 3-5x faster than host writes predict, write amplification is the likely cause.

Vendor quirks and known anomalies

Samsung EVO anomaly report. An observed Samsung 970 EVO Plus 2TB (rated 1200 TBW, firmware 2B2QEXM7) reported 100% Percentage Used at 369 TB written, roughly 31% of rated endurance, while Available Spare remained 100%. Samsung’s firmware may use a different baseline or calculation than a simple linear mapping to TBW. If you see 100% on a Samsung EVO with low Data Units Written and full Available Spare, treat the field with skepticism and rely on Available Spare and Media Errors instead. The specification intentionally leaves the calculation vendor-specific.

255 is the maximum reportable value. The specification states that percentages greater than 254 shall be represented as 255. A drive showing 255% has consumed at least the vendor-defined endurance reference represented by 255%; the underlying estimate is vendor-specific.

The field is vendor-specific by design. The specification does not mandate a formula. Two drives from different manufacturers with identical host write histories can show different Percentage Used values.

Action thresholds

Percentage Used	Severity	Action
Below 80%	INFO	Baseline tracking. No action.
80-90%	PLAN	Begin procurement of replacement drives.
90-100%	TICKET	Plan specific replacement date. Order if not already in inventory.
Above 100%	TICKET	Replace as soon as practical. Not an emergency unless other signals corroborate.
Above 100% with Available Spare below threshold	Escalate	End of life with depleted spare capacity. Prioritize replacement.
Above 100% with Media Errors increasing	Escalate	Active data loss. Replace immediately.

Percentage Used above 100% alone does not justify paging someone at 3 a.m. The drive may operate normally for months. But it does justify a replacement ticket with a defined timeline, not a “monitor and see” deferral.

Reading the values with smartctl

# All NVMe health attributes
smartctl -a /dev/nvme0n1

# Percentage Used specifically
smartctl -A /dev/nvme0n1 | grep "Percentage Used"

# Available Spare and threshold
smartctl -A /dev/nvme0n1 | grep "Available Spare"

# Media errors
smartctl -A /dev/nvme0n1 | grep "Media and Data Integrity Errors"

# Data Units Written (host write volume)
smartctl -A /dev/nvme0n1 | grep "Data Units Written"

# Critical Warning bits (0x00 = none, 0x01 = spare low, 0x04 = reliability, 0x08 = read-only)
smartctl -A /dev/nvme0n1 | grep "Critical Warning"

Read these as a group, not filtered for a single value.

For automated monitoring, smartmontools 7.5 (2025-04-30) added experimental smartd -u reporting for NVMe Percentage Used and Media and Data Integrity Errors.

Signals to watch in production

Signal	Why it matters	Warning sign
Percentage Used rate of change	Projects end-of-warranty date; detects write amplification acceleration	Sudden acceleration without workload change
Available Spare	Direct measure of remaining bad-block replacement capacity	Any sustained decline, especially below vendor threshold
Available Spare Threshold	Vendor-set floor below which Critical Warning bit 0 fires	Drive reporting below this value has set the spare warning
Media and Data Integrity Errors	Confirmed uncorrectable data corruption	Any increase from baseline
Critical Warning bits	Drive firmware’s own escalation signal	Bit 0 (spare low), bit 2 (reliability degraded), bit 3 (read-only)
Data Units Written	Raw host write volume for endurance runway calculation	Sustained high rate relative to rated TBW
Composite Temperature	Heat accelerates NAND wear and data retention loss	Sustained operation above WCTEMP (typically 70-80C)

How Netdata helps

Netdata’s smartctl collector surfaces Percentage Used, Available Spare, Media and Data Integrity Errors, Critical Warning bits, and Data Units Written as per-second metrics with anomaly detection on each signal.

Correlation across the cascade: View all three endurance signals on the same dashboard. The relationship between Percentage Used, Available Spare, and Media Errors is more diagnostic than any one alone.
Rate-of-change tracking: Per-second derivatives on counter metrics show the rate of Percentage Used increase without manual diffing. Acceleration without a workload change suggests write amplification or firmware anomaly.
Critical Warning bit decomposition: Each bit tracked independently, so alerts distinguish “spare below threshold” (bit 0) from “reliability degraded” (bit 2) from “read-only” (bit 3) without decoding hex.
Fleet-level anomaly detection: When multiple NVMe drives of the same model show Percentage Used climbing faster than expected, anomaly detection surfaces the pattern across hosts, not just per-drive.
Temperature correlation: Composite Temperature alongside Percentage Used rate of change isolates thermal causes of accelerated wear.