IBM 000-8697 Manual Do Utilizador

Installation and Initial Configuration

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.

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

 for more

information about fast recovery. Refer to

for detailed information

about the physical log.

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

 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.