DB2 Version 9.7 for Linux, UNIX, and Windows

mirrorlogpath - Mirror log path configuration parameter

This parameter allows you to specify a string of up to 242 bytes for the mirror log path. The string must point to a path name, and it must be a fully qualified path name, not a relative path name.

Configuration type: Database
Parameter type: Configurable
Default [range]: Null [any valid path or device]

Note: In a single or multi-partition DB2® ESE environment, the node number is automatically appended to the path. This is done to maintain the uniqueness of the path in multiple logical node configurations.

If mirrorlogpath is configured, DB2 will create active log files in both the log path and the mirror log path. All log data will be written to both paths. The mirror log path has a duplicated set of active log files, such that if there is a disk error or human error that destroys active log files on one of the paths, the database can still function.

If the mirror log path is changed, there might be log files in the old mirror log path. These log files might not have been archived, so you might need to archive these log files manually. Also, if you are running replication on this database, replication might still need the log files from before the log path change. If the database is configured with the User Exit Enable (userexit) database configuration parameter set to Yes, and if all the log files have been archived either by DB2 automatically or by yourself manually, then DB2 will be able to retrieve the log files to complete the replication process. Otherwise, you can copy the files from the old mirror log path to the new mirror log path.

If logpath or newlogpath specifies a raw device as the location where the log files are stored, mirror logging, as indicated by mirrorlogpath, is not allowed. If logpath or newlogpath specifies a file path as the location where the log files are stored, mirror logging is allowed and mirrorlogpath must also specify a file path.

Recommendation: Just like the log files, the mirror log files should be on a physical disk that does not have high I/O.

It is strongly recommended that this path be on a separate device than the primary log path.

You can use the database system monitor to track the number of I/Os related to database logging.

The following data elements return the amount of I/O activity related to database logging. You can use an operating system monitor tool to collect information about other disk I/O activity, then compare the two types of I/O activity.

log_reads (number of log pages read)
log_writes (number of log pages written).