IBM AIX 7.3 – Common Problem 167 – 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

Database write throughput plateaus far below storage capability. iostat shows queues but CPU is idle, indicating AIO server starvation.

Environment & Reproduction

Common on Oracle and DB2 LPARs using JFS2 with default AIO settings.

ioo -L aio_maxreqs
oslevel -s
uname -a

Root Cause Analysis

Cause is aio_maxservers and aio_minservers set too low for the workload; AIO server processes cannot keep up with submitted requests.

Quick Triage

Inspect AIO usage and current limits.

ioo -L aio_maxreqs

Step-by-Step Diagnosis

Capture deeper evidence to isolate the failure path.

ioo -L aio_maxreqs
pstat -a | grep aio | wc -l
lsattr -El aio0
iostat -a 2 5
ps -ek | grep aios

Solution – Primary Fix

Apply the proven primary fix in a controlled change window.

ioo -p -o aio_maxservers=200
ioo -p -o aio_minservers=10
ioo -p -o aio_maxreqs=65536
bosboot -ad /dev/ipldevice

Solution – Alternative Approaches

Use these alternatives when the primary fix is blocked by environmental constraints.

lsattr -El posix_aio0
chdev -l posix_aio0 -a maxservers=200 -P
shutdown -Fr

Verification & Acceptance Criteria

Confirm the system meets acceptance criteria after the change.

iostat 2 5
pstat -a | grep aios | wc -l
ioo -a | grep aio

Rollback Plan

Revert cleanly if regressions appear during validation.

ioo -d aio_maxservers
ioo -d aio_minservers
shutdown -Fr

Prevention & Hardening

Reduce recurrence with monitoring and preventive tuning.

topasrec -L
nmon -f -s 60 -c 30
emgr -l

Related Errors & Cross-Refs

Related to JFS2 log contention, fcs adapter queue depth, and CPU folding.

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 AIX 7.3 Performance Management, ioo and Oracle on AIX best practices.