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 Intent Log

VxFS reduces system failure recovery times by tracking file system activity in the VxFS intent log. This feature records pending changes to the file system structure in a circular intent log. The intent log recovery feature is not readily apparent to users or a system administrator except during a system failure. 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. Replaying the intent log may not completely recover the damaged file system structure if there was a disk hardware failure; hardware problems may require a complete system check using the fsck utility provided with VxFS.

Intent Log Resizing

The VxFS intent log is allocated when the file system is first created. The size of the intent log is based on the size of the file system---the larger the file system, the larger the intent log. The maximum default intent log size for disk layout Versions 4, 5, and 6 is 16 megabytes.

With the Version 6 disk layout, you can dynamically increase or decrease the intent log size using the logsize option of the fsadm command. Increasing the size of the intent log can improve system performance because it reduces the number of times the log wraps around. However, increasing the intent log size can lead to greater times required for a log replay if there is a system failure.

See the mkfs_vxfs(1M) and the fsadm_vxfs(1M) manual pages for more information on intent log size.