Symantec logo

Logging

A key aspect of any file system is how to recover if the system experiences a system crash. Earlier methods required a time-consuming scan of the entire file system. A better solution is the method logging (or journaling) the metadata of files. With logging, whenever something changes in the metadata of a file, this new attribute information will be logged into a reserved area of the file system. Only after the write of the metadata to the log is complete, will the file system write the actual data to disk. If and when a system crash occurs, the system recovery code will analyze the metadata log and try to clean up only those files. Without logging, a file system check (fsck) must look at all of the metadata.

Intent logging minimizes system downtime after abnormal shutdowns by logging filesystem transactions. When the system is halted unexpectedly, this log can be replayed and outstanding transactions completed. The check and repair time for filesystems can be reduced to a few seconds, regardless of the filesystem size.

See "About VxFS intent log" on page 17.

By default, VxFS filesystems log file transactions before they are committed to disk, reducing time spent checking and repairing filesystems after the system is halted unexpectedly.