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Installation and Initial Configuration 1-25
Physical Log Configuration Guidelines
MIRROROFFSET
The MIRROROFFSET parameter specifies the offset into the disk partition or
into the device to reach the chunk that serves as the mirror for the root
dbspace initial chunk. Leave this worksheet field blank until you allocate
OnLine disk space.
Physical Log Configuration Guidelines
This section describes how to assign values to the physical log parameters.
The physical log is a block of contiguous disk space that serves as a storage
area for copies of unmodified disk pages. The physical log is a component of
OnLine fast recovery, a fault-tolerant feature that automatically recovers
OnLine data in the event of a system failure. Refer to page 4-39 for more
information about fast recovery. Refer to page 2-152 for detailed information
about the physical log.
PHYSDBS
PHYSDBS specifies the name of the dbspace that contains the physical log.
For the initial configuration, the physical log must be created in the initial
chunk of the root dbspace. For this reason, you do not specify PHYSDBS as
part of the configuration. It is assigned by default to the value of ROOTNAME.
After additional dbspaces have been defined, you can move the physical log
to another dbspace to reduce disk contention.
PHYSFILE
PHYSFILE specifies the size of the physical log in kilobytes. A general
guideline for sizing your physical log is that the size of the physical log
should be about twice the size of one logical log file.
A more precise guideline is that total disk space allocated to the physical log
and the logical log files should equal about 20 percent of all dbspace
dedicated to OnLine. The ratio of logical log space to physical log space
should be about 3:1.