I was dealing with an aging 4 TB Western Digital Green HDD with about 86 000 power-on hours that began reporting SMART warnings (C5 - "Current Pending Sector Count" and C6 - "(Offline) Uncorrectable Sector Count"). The drive only showed errors once it was filled beyond +-75% capacity.
Normally, the common response would be "replace the drive immediately." While replacement is inevitable, I wanted to understand the failure mode, preserve safe capacity, and reduce risk in the interim to simulate a scenario where budget constraints are a reality.
Initial Findings
SMART diagnostics revealed:
- C5 ("Current Pending Sector Count"): non-zero
- C6 ("(Offline) Uncorrectable Sector Count"): non-zero but stable
- C4 ("Reallocation Event Count"): zero
This suggested that it was localised surface degradation, not a rapidly collapsing disk.
Hypothesis
On large, aging HDDs, surface degradation often appears first on inner tracks where there is lower linear velocity and tighter ECC margins. If my hypothesis was true, constraining use to the outer tracks could stabilise the drive.
Methodology
- SMART analysis pre-format:
- Get C4, C5, and C6 data.
- Full destructive write test:
- Delete existing partition.
- Perform a full (non-quick) NTFS full-disk format with the default 4096 sector size to force sector re-evaluation.
- SMART analysis post-format:
- Get C4, C5, and C6 data.
- Verify pending sectors were resolved.
- Confirm no new uncorrectable writes occurred.
- Capacity derating:
- Reduce the partition size to 50% of the disk (I could've used 75%, but I chose to be safe.)
- Perform a full (non-quick) NTFS full-disk format again with the default 4096 sector size to force sector re-evaluation.
- Validation:
- Get C4, C5, and C6 data to monitor for regression
Results
- Post-mitigation SMART status:
- Pending sectors: 0
- Reallocated sectors: 0
- Uncorrectable sectors: unchanged and stable
- Write error rate: stable
- No I/O errors during sustained writes
The failure was successfully isolated and the remaining surface proved stable under load.
Outcome
The drive is now reclassified from
"Not suitable for backups or irreplaceable data"
to
"Acceptable for scratch space, media, and data you're OK to lose if you don't have a backup"
Additionally, I automated SMART monitoring at every boot and only triggered alerts on regression from a baseline.
Key Takeaways
- Hardware failures are often partial, not binary.
- Hardware can be repurposed, not immediately thrown away, reducing costs and also e-waste.
- Evidence-driven diagnostics enable risk-aware decisions.
- Capacity derating is a legitimate professional technique when paired with monitoring.
- The goal is not perfection, but controlled risk and predictability.
This approach mirrors how degraded components are handled in professional infrastructure environments:
constrain,
monitor, and
plan replacement,
rather than panic or ignore warning signs.
