Fast File System Recovery

Most file systems rely on full structural verification by the fsck utility as the only means to recover from a system failure. For large disk configurations, this involves a time-consuming process of checking the entire structure, verifying that the file system is intact, and correcting any inconsistencies.

VxFS provides recovery only seconds after a system failure by utilizing a tracking feature called intent logging. This feature records pending changes to the file system structure in a circular intent log. During system failure recovery, the VxFS fsck utility performs an intent log replay, which scans the intent log and nullifies or completes file system operations that were active when the system failed. The file system can then be mounted without completing a full structural check of the entire file system. The intent log recovery feature is not readily apparent to the user or the system administrator except during a system failure.

Replaying the intent log may not completely recover the damaged file system structure if the disk suffers a hardware failure; such situations may require a complete system check using the fsck utility provided with VxFS.