Configuration

You can control the balance between performance and robustness on either a global or per-file basis.

• Specifying the O_SYNC bit when opening a file causes all I/O operations on that file (both data and metadata) to be performed synchronously.

  The fsync() and sync() functions let you flush the filesystem write-behind cache on demand; otherwise, any dirty data is flushed from cache under the control of the global blk delwri= option (the default is two seconds—see io-blk.so in the Utilities Reference).

• You control the global configuration with the commit= option, either to io-blk.so as an option to apply to all filesystems, or via the mount command as an option to apply to a single instance of a mounted filesystem). The levels are none, low, medium, and high, which differ in the degree in which metadata is written synchronously versus asynchronously, or even time-delayed.
  Note: At any level less robust than the default (that is, medium), the filesystem doesn't guarantee the same level of integrity following an unexpected power loss, because multiple-block updates might not be ordered correctly.