AIX > Administrator > Performance

Tuning a Perfect Note

A look at performance tuning and new AIX 5.3 commands.

A look at performance tuning and new AIX 5.3 commands.


By default, AIX is a smooth-running system. However, it benefits from some help. In this article, I have touched on some of the more important tuning variables, some of the new commands and how our recommendations are changing. In addition to the "Reference" sidebar, be sure to review the starter set of tunables for your system provided in the sidebar above. Please keep in mind that these should be tested and your mileage may vary.

Helpful Links

1. Lparmon -
2. Nmon -
3. Nmon Analyser -
4. Instructions for running the performance script and the script itself can be found at and
5. Jaqui's AIX* Blog, which has a base set of performance tunables for AIX 5.3 -
6. vmo command -

7. ioo command -

8. vmstat command -

9. lvmo command -


Starter set of tuneables
Current recommended AIX* 5.3 Performance Parameters: Please ensure you test these first before implementing in production as your mileage may vary

no -p -o rfc1323=1
no -p -o sb_max=1310720
no -p -o tcp_sendspace=262144
no -p -o tcp_recvspace=262144
no -p -o udp_sendspace=65536
no -p -o udp_recvspace=655360
nfso -p -o rfc_1323=1
nfso -p -o nfs_socketsize=60000
nfso -p -o nfs_tcp_socketsize=600000

Memory Settings
vmo -p -o minperm%=5
Leave maxperm and maxclient at default of 80
Leave strict_maxperm and strict_maxclient at their defaults

vmo -p -o minfree=960
vmo -p -o maxfree=1088
vmo -p -o lru_file_repage=0
vmo -p -o lru_poll_interval=10

IO Settings
Leave mipgahead and J2_minPageReadAhead at their defaults of 2
ioo -p -o j2_maxPageReadAhead=128
ioo -p -o maxpgahead=16
ioo -p -o j2_maxRandomWrite=32
ioo -p -o maxrandwrt=32
ioo -p -o j2_nBufferPerPagerDevice=1024
ioo -p -o pv_min_pbuf=1024
ioo -p -o numfsbufs=2048

If doing lots of raw I/O you may want to change lvm_bufcnt
Default is 9
ioo -p -o lvm_bufcnt=12

Others left to default that you may want to tweak include:
ioo -p -o numclust=1
ioo -p -o j2_nRandomCluster=0
ioo -p -o j2_nPagesPerWriteBehindCluster=32

These are starting points only.

Jaqui Lynch is an independent consultant, focusing on enterprise architecture, performance and delivery on Power Systems with AIX and Linux.

comments powered by Disqus



2019 Solutions Edition

A Comprehensive Online Buyer's Guide to Solutions, Services and Education.

Achieving a Resilient Data Center

Implement these techniques to improve data-center resiliency.


AIO: The Fast Path to Great Performance

AIX Enhancements -- Workload Partitioning

The most exciting POWER6 enhancement, live partition mobility, allows one to migrate a running LPAR to another physical box and is designed to move running partitions from one POWER6 processor-based server to another without any application downtime whatsoever.

IBM Systems Magazine Subscribe Box Read Now Link Subscribe Now Link iPad App Google Play Store
IBMi News Sign Up Today! Past News Letters