System Administration Guide
Chapter 2, Administering filesystems

Forced data writes to disk

Forced data writes to disk

Sync-on-close ensures that all files modified by a process are written back to the disk when they are closed. This minimizes data loss in the event of power failure.

In addition, the filesystem is transitioned to a quiescent state every second. DTFS does not depend on the standard filesystem flusher functionality (bdflush) to synchronize user data; it does this itself.

In addition, a feature called ``shadow paging'' ensures that new file data is first written to shadow blocks, leaving the original blocks unmodified. If a system failure occurs before the new data is written to disk, the original data is still intact because the blocks were not freed.

These features mean that as soon as you have saved the file, you can switch off the power and the file will be on the disk. This is particularly useful in desktop and laptop environments.

WARNING: Some caching disk controllers use write-back caching techniques that nullify the improved data reliability and integrity provided by DTFS. If this is the case, data integrity cannot be guaranteed. However, controllers that use write-through caching take advantage of DTFS features.

If your controller supports both caching techniques, configure it to use write-through caching.

If sync-on-close is enabled, it will noticeably degrade your overall system performance because of the time spent writing to the disk.