Direct I/O - Red Hat GLOBAL FILE SYSTEM 5.0 Manual

MountPoint
Specifies the directory where the GFS file system is mounted.
Device
Specifies the device node of the file system.
Table 4.4, "GFS-specific Options Available When Adding Journals"
options that can be used when adding journals to a GFS file system.
Flag Parameter
-h
-J MegaBytes
-j Number
-T
-q
-V
-v
Table 4.4. GFS-specific Options Available When Adding Journals

7. Direct I/O

Direct I/O is a feature of the file system whereby file reads and writes go directly from the
applications to the storage device, bypassing the operating system read and write caches.
Direct I/O is used only by applications (such as databases) that manage their own caches.
An application invokes direct I/O by opening a file with the
can attach a direct I/O attribute to a file, in which case direct I/O is used regardless of how the
file is opened.
Description
Help. Displays short usage message.
Specifies the size of the new journals in megabytes.
Default journal size is 128 megabytes. The minimum
size is 32 megabytes. To add journals of different
sizes to the file system, the
must be run for each size journal. The size specified
is rounded down so that it is a multiple of the
journal-segment size that was specified when the file
system was created.
Specifies the number of new journals to be added by
the command. The default value is 1.
gfs_jadd
Test. Do all calculations, but do not write any data to
the disk and do not add journals to the file system.
Enabling this flag helps discover what the
command would have done if it were run without this
flag. Using the flag with the
-v
verbosity level to display more information.
Quiet. Turns down the verbosity level.
Displays command version information.
Turns up the verbosity of messages.
O_DIRECT
Direct I/O
describes the GFS-specific
command
gfs_jadd
gfs_jadd
flag turns up the
-T
flag. Alternatively, GFS
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