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Oracle Tips by Burleson |
Disk I/O Tuning
Chapter 3:
SCSI Tuning Under AIX
You
should also note that the original RS/6000 SCSI adapter does not
support queuing. It is inappropriate to attach a disk array device
to such an adapter.
Controlling the Number of System pbufs in AIX
In
AIX the Logical Volume Manager (LVM) uses a construct called a "pbuf"
to control a pending I/O to disk. In AIX Version 3, one pbuf is
required for each page being read or written. In systems that do
large amounts of sequential I/O, this can result in depletion of the
pool of pbufs. The vmtune command can be used to increase
the number of pbufs to compensate for this effect.
In
AIX Version 4, only a single pbuf is used for each sequential I/O
request, regardless of the number of pages involved. This
greatly decreases the probability of running out of pbufs and tuning
pbufs in version 4 and is generally not advised.
In
AIX Version 5, you no longer need to adjust this parameter.
The above text is
an excerpt from:
Oracle Disk I/O Tuning
Disk IO Performance & Optimization for Oracle
Databases
ISBN
0-9745993-4-4
by Mike Ault
Oracle Consulting
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