Red Hat GLOBAL FILE SYSTEM 4.7, Manual

Page: 46 / 60

In this example, the command sets the
inherit_directio
flag on the directory named
/gfs1/data/
.
gfs_tool setflag inherit_directio /gfs1/data/
8. 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.
Usage
Setting and Clearing the
inherit_jdata
Flag
gfs_tool setflag inherit_jdata Directory
gfs_tool clearflag inherit_jdata Directory
Setting and Clearing the
jdata
Flag
gfs_tool setflag jdata File
gfs_tool clearflag jdata File
Directory
Specifies the directory where the flag is set or cleared.
File
Chapter 4. Managing GFS
34