7.3. File Systems

For very large file systems, the mkfs.ext4 process can take a very long time to initialize all inode tables in the file system. This process can be deferred with the -E lazy_itable_init=1 option. If this is used, kernel processes will continue to initialize the file system after it is mounted. The rate at which this initialization occurs can be controlled with the -o init_itable=n option for the mount command, where the amount of time spent performing this background initialization is roughly 1/n. The default value for n is 10.

Because some applications do not always properly fsync() after renaming an existing file, or truncating and rewriting, ext4 defaults to automatic syncing of files after replace-via-rename and replace-via-truncate operations. This behavior is largely consistent with older ext3 filesystem behavior. However, fsync() operations can be time consuming, so if this automatic behavior is not required, use the -o noauto_da_alloc option with the mount command to disable it. This will mean that the application must explicitly use fsync() to ensure data persistence.

By default, journal commit I/O is given a slightly higher priority than normal I/O. This priority can be controlled with the journal_ioprio=n option of the mount command. The default value is 3. Valid values range from 0 to 7, with 0 being the highest priority I/O.