IBM AIX 7.3 – Common Problem 145 – 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

`iostat -DRTl` shows `serv qfull` >0 and `avgwait` climbing into hundreds of ms.

Environment & Reproduction

AIX 7.3 database LPAR with default `queue_depth=20` on enterprise SAN LUNs.

Root Cause Analysis

Workload queue depth exceeds the configured `queue_depth` and `num_cmd_elems` on fcs.

Quick Triage

Run `iostat -DRTl 2 5`, `lsattr -El hdiskN`, and `fcstat fcs0 | grep `’Elements’.

Step-by-Step Diagnosis

Capture `pmstat`, `topas -D`, and `errpt | grep SC_DISK` for context.

Solution – Primary Fix

Raise depth: `chdev -l hdiskN -a queue_depth=64 -P` and reboot or `varyoffvg`+`cfgmgr`.

Solution – Alternative Approaches

Tune fcs: `chdev -l fcs0 -a num_cmd_elems=2048 -a max_xfer_size=0x200000 -P`.

Verification & Acceptance Criteria

`iostat -DRTl` shows `qfull=0` and `avgwait` returns under 5 ms during peak load.

Rollback Plan

Revert `queue_depth` and `num_cmd_elems` to previous values with `chdev -P`.

Prevention & Hardening

Document storage-vendor-recommended `queue_depth` per array model and apply via `chdev -P`.

Related Errors & Cross-Refs

Related to `SC_DISK_ERR4`, `FCP_ARRAY_ERR2`, and slow `db2`/`Oracle` writes.

Related tutorial: View the step-by-step tutorial for aix-7.3.

View all aix-7.3 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

IBM Docs: AIX SAN tuning, `iostat -D`, fcs adapter tunables.