Data Journaling - Red Hat ENTERPRISE LINUX 5 - GLOBAL FILE SYSTEM Manual

Data Journaling

Usage
Setting the inherit_directio flag
gfs_tool setflag inherit_directio Directory
Clearing the inherit_directio flag
gfs_tool clearflag inherit_directio Directory
Directory
Specifies the directory where the inherit_directio flag is set.
Example
In this example, the command sets the inherit_directio flag on the directory named /mnt/gfs/
data.
gfs_tool setflag inherit_directio /mnt/gfs/data
This command displays the flags that have been set for the /mnt/gfs/data directory. The full output
has been truncated.
[root@tng3-1 gfs]# gfs_tool stat /mnt/gfs/data
...
Flags:
inherit_directio
3.10. Data Journaling
Ordinarily, GFS writes only metadata to its journal. File contents are subsequently written to disk by
the kernel's periodic sync that flushes file system buffers. An fsync() call on a file causes the file's
data to be written to disk immediately. The call returns when the disk reports that all data is safely
written.
Data journaling can result in a reduced fsync() time, especially for small files, because the file data
is written to the journal in addition to the metadata. An fsync() returns as soon as the data is written
to the journal, which can be substantially faster than the time it takes to write the file data to the main
file system.
Applications that rely on fsync() to sync file data may see improved performance by using data
journaling. Data journaling can be enabled automatically for any GFS files created in a flagged
directory (and all its subdirectories). Existing files with zero length can also have data journaling turned
on or off.
Using the gfs_tool command, data journaling is enabled on a directory (and all its subdirectories)
or on a zero-length file by setting the inherit_jdata or jdata attribute flags to the directory or file,
respectively. The directory and file attribute flags can also be cleared.
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