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Oracle Tips by Burleson |
Disk I/O Tuning
Chapter 3:
HP-UX SCSI Tuning
Much
like SUN Solaris, HP has several kernel based tuning parameters that
are used to adjust the behavior of to SCSI interface, bus and
device.
Probably, the most important is scsi_max_qdepth.
scsi_max_qdepth - This is the maximum number of I/Os that a single
SCSI target will queue up for execution. The parameters has a
minimum value of 1, a default set value of 8, and a maximum value of
255.
Some
SCSI devices support tagged queuing, which means they can have more
than one SCSI command outstanding at any point in time. The number
of commands that can be outstanding varies by device and is not
known to HP-UX. To avoid overflowing this queue, HP-UX will not
send more than a certain number of outstanding commands to any SCSI
device. This tunable sets the default value for that limit. The
default value can be overridden for specific devices using ioctl.
The ioctl is a device interface system control that allows commands
to be issued to alter specific setpoints on devices; it is not a
command line program.
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
Services
Burleson
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