IBM AIX 7.2 – Common Problem 126 – Diagnosis and Fix

📖 ~1 min read

Table of contents

1. Symptom & Impact
2. Environment & Reproduction
3. Root Cause Analysis
4. Quick Triage
5. Step-by-Step Diagnosis
6. Solution – Primary Fix
7. Solution – Alternative Approaches
8. Verification & Acceptance Criteria
9. Rollback Plan
10. Prevention & Hardening
11. Related Errors & Cross-Refs
12. References & Further Reading

Symptom & Impact

`errpt` reports `DISK_ERR4` and `PATH_HAS_FAILED` and I/O latency spikes on hdisk LUNs.

Environment & Reproduction

AIX 7.2 LPAR on Power9 with dual VIOS NPIV fabric after a SAN switch firmware update.

Root Cause Analysis

One fabric path is missing or in `Failed` state in `lspath` due to fcs adapter reset.

Quick Triage

Run `errpt -a | more`, `lspath -l hdiskN` and `fcstat fcs0` to see link drops.

Step-by-Step Diagnosis

`lspath -l hdiskN -F’name parent path_status status’` shows `Failed` on a fcsX path.

Solution – Primary Fix

Re-enable the path: `chpath -l hdiskN -p fscsiX -s enable` then `cfgmgr -v`.

Solution – Alternative Approaches

Remove and rediscover the dead path: `rmpath -l hdiskN -p fscsiX -d` followed by `cfgmgr`.

Verification & Acceptance Criteria

All paths show `Enabled` in `lspath` and `errpt` stops generating `PATH_HAS_FAILED` entries.

Rollback Plan

Re-disable the path with `chpath -l hdiskN -p fscsiX -s disable` if it destabilises traffic.

Prevention & Hardening

Enable `dyntrk=yes` and `fc_err_recov=fast_fail` on every fscsiX device permanently.

Related Errors & Cross-Refs

Often pairs with `SC_DISK_ERR2` from MPIO and VIOS `vfc_err` events.

Related tutorial: View the step-by-step tutorial for aix-7.2.

View all aix-7.2 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

IBM Docs: MPIO PCM, `lspath`, `chpath`, and Power9 NPIV best practices.