ATA uncorrectable sectors and read errors · Linux Fix Lab

Symptoms & scope

The same file or region repeatedly returns a read error.
ATA logs include UNC rather than only a link reset.

Relevant environment

ATA disks and SSDs reporting libata errors; SMART support varies with bridges and vendors.

Recognizable messages (synthetic examples)

ata3.00: error: { UNC }

Preserve data and inspect the failing read/LBA; the line does not establish which files were damaged.

Possible causes

These are possible explanations, not a confirmed diagnosis. Several independent faults can coexist.

UNC means the device could not recover data after its internal retries; media deterioration or drive firmware may be involved.
Filesystem errors can be downstream effects of unreadable sectors, while independent memory or transport faults still need separate evidence.

Diagnose safely

Run one command at a time in the relevant session. Read the explanation first. Uppercase placeholders need your own values; tools and privileges vary by distribution. These commands are displayed here and never executed by the website.

Check 1

Read the kernel log with journal privileges if needed, retaining command, LBA and drive context.

journalctl -k -b --no-pager -n 300

Interpret the result: Repeated UNC at the same LBA is more specific than application EIO. ICRC points to transport corruption and needs a different investigation.

Check 2

Replace /dev/sdX with the whole affected disk; read attributes and existing test/error logs only.

sudo smartctl -x /dev/sdX

Interpret the result: Pending, offline-uncorrectable or growing reallocated counts strengthen the media-fault concern. Vendor attributes and an overall PASS result are not a complete integrity test.

Evidence-guided next steps

Preserve data before repair

If important data is not backed up and UNC recurs, stop avoidable writes. Recover the most valuable readable files or make an error-tolerant rescue image to a different healthy device; seek specialist recovery when the drive becomes mechanically unstable.

Precautions: Do not run destructive bad-block tests or repeatedly scan a failing disk before securing data. A rescue destination must never be the source.

Recovery / rollback: Keep the original powered down after imaging. Recovery work can be repeated on a copy without overwriting the source.

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Replace media when evidence persists

If unreadable LBAs or health counters continue growing on a verified data path, replace the drive and restore from a checked backup or rescued image. Run filesystem verification on the replacement copy before returning it to service.

Precautions: A filesystem repair cannot make damaged media reliable. Confirm restored files independently where checksums or original copies exist.

Recovery / rollback: Retain the original and backup until restoration is verified; do not erase the only remaining copy.

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References & review

This guide was prepared from primary project or distribution sources and reviewed on the date shown. This is an editorial source check, not evidence that a fix was reproduced on your hardware. Diagnostic log examples are synthetic fixtures. Version-dependent details must be checked against your installed release.

Linux kernel: libata ATA errors and recovery (project or distribution documentation)
smartmontools: smartctl manual source (project or distribution documentation)

Related hardware and driver context

These profiles explain relevant driver paths. They do not establish that your device has this fault. Identify your device and binding first.

Identify hardware locally