EMEN2 Maintenance and Backups

EMEN2 supports three types of backups: Log Archive, Cold Backup, and Hot Backup.

Log Archive

Berkeley DB provides guarantees about atomicity and durability by first writing changes to a series of log files. A transactions is not marked as committed until it has been flushed to stable storage. This allows recovery from a crash without loss of data.

In the event of a crash or hardware failure, the log files will be examined. All committed transactions will be written out to the BTree files (in $DB_HOME/data) and any uncommitted transactions will be aborted.

The log files are stored in $DB_HOME/log as log.XX, where XX is a sequential integer starting from 1. With default settings, the files are 8 MB each. As one log file is finished, the next log file in the sequence is created and used as the active log file.

Log files that are not being used by any open transaction may be archived after a "Checkpoint" is made. This frees up disk space in the DB_HOME environment, and lets the administrator move the logs to long term archival storage.

.. more to come ..