Size and location of the physical log
When the database server initializes disk space, it places the physical log in the root dbspace. The initial size of the physical log is set by the PHYSFILE configuration parameter.
After you initialize the database server for the first time, you can change the size or location of the physical log with the onparams utility.
To improve performance (specifically, to reduce the number of writes to the root dbspace and minimize disk contention), you can move the physical log out of the root dbspace to another dbspace, preferably to a disk that does not contain active tables or the logical-log files. For best performance, create the plogspace to store the physical log and allow the database server to expand the size of the physical log as needed to improve performance.