Creation of a mirror chunk

When you specify a mirror chunk, the database server copies all the data from the primary chunk to the mirror chunk. This copy process is known as recovery. Mirroring begins as soon as recovery is complete.

The recovery procedure that marks the beginning of mirroring is delayed if you start to mirror chunks within a dbspace that contains a logical-log file. Mirroring for dbspaces that contain a logical-log file does not begin until you create a level-0 backup of the root dbspace. The delay ensures that the database server can use the mirrored logical-log files if the primary chunk that contains these logical-log files becomes unavailable during a dbspace restore.

The level-0 backup copies the updated database server configuration information, including information about the new mirror chunk, from the root dbspace reserved pages to the backup. If you perform a data restore, the updated configuration information at the beginning of the backup directs the database server to look for the mirrored copies of the logical-log files if the primary chunk becomes unavailable. If this new storage-space backup information does not exist, the database server is unable to take advantage of the mirrored log files.

For similar reasons, you cannot mirror a dbspace that contains a logical-log file while a dbspace backup is being created. The new information that must be in the first block of the dbspace backup tape cannot be copied there after the backup has begun.

For more information about creating mirror chunks, see Using mirroring.