Oracle database servers on IBM Power@AIX can have a really performance boost when VMM tuned upon the default IBM Settings.
AIX 5.2 VMM Parameters Tunning
vmtune -c8 -s1 -r32 -R64 -p5 -P20 -t20 -f128 -F144 -W32
setting maxfree to 144
Setting minfree to 128
Setting minperm% to 5
Setting maxperm% to 20
Setting maxclient% to 20
Setting minpgahead to 32
Setting maxpgahead to 64
Setting maxrandwrt to 32
Setting numclust to 8
Setting sync_release_ilock to 1
async io servers : maxservers = 10 * CPU, minservers=maxservers/2
The above parameters are a good starting point. You can tune a little bit by monitoring performance.
If your database is an OLTP system , using lots of db_sequential_reads (index scans) you can put minpgahead to 512 and maxpgahead to 1024 on JFS and JFS2 volume groups.
For async io you can use the disks rule of thumb: maxservers=10*[total_disks_for_oracle_files],minservers=maxservers/2
On AIX 5.3 there is a slight diference in the way the VMM works so you can use this settings:
vmo -r -o lgpg_size=16777216 lgpg_regions=128
vmo -p -o minperm%=5
vmo -p -o maxperm%=90
vmo -p -o maxclient%=90
vmo -p -o lru_file_repage=0
vmo -p -o minfree=960
vmo -p -o maxfree=1088
For async io as for AIX 5.2.
Oracle Parameters for 9iR2(126.96.36.199) and up :
filesystem_options=SETALL Enables both ASYNC and DIRECT I/O or CONCURRENT I/O(JFS2)
It is advisable not to use direct I/O because degrades performance. If you have only JFS filesystems then use filesystem_options=ASYNC which is the default setting.
There is no "built-in" support for CIO or DIO in Oracle Database 9iR2 (9.2.0) or lower, though you can force the use of CIO (JFS2) or DIO (JFS) with filesystem mount options.