Questions On /etc/fstab

[Hill_1]

Dear all,
May I know what is the delaylog for the option field in /etc/fstab?
Thanks in advanced.

[Frederic Sevestre]

Hi ,
You can find all informations about differents mount options with the man mount_vxfs.
Regards
Fr??d??ric

[Thierry Poels_1]

Hi,

see "man mount_vxfs"

Controls intent logging. File system integrity across system failure requires that logging be enabled. The default is "log". In log mode, file system structural
changes are logged to disk before the system call returns to the application. If the system crashes, fsck_vxfs(1M) will complete logged operations that
have not completed.

In delaylog mode, some system calls return before the intent log is written. This improves the performance of the system, but some changes are not guaranteed until a short time later when the intent log is written. This mode approximates traditional UNIX system guarantees for correctness in case of system failures.


regards,
Thierry.

[Animesh Chakraborty · Accepted solution]

Hi Hill,
VxFS offers mount options to delay or disable transaction logging, and to
control whether user data is written synchronously or delayed. This allows
the system administrator to make trade-offs between file system integrity
and performance, guaranteeing the integrity of critical file systems, while
optimizing the performance of non-critical or temporary file systems.

Logging Options

These options control how transactions are logged to disk:

1. Full Logging (log)

File system structural changes are logged to disk before the system
call returns to the application. If the system crashes, fsck(1M) will
complete logged operations that have not completed.

2. Delayed Logging (delaylog)

Some system calls return before the intent log is written. This
improves the performance of the system, but some changes are not
guaranteed until a short time later when the intent log is written.
This mode approximates traditional UNIX system guarantees for
correctness in case of system failure.

3. Temporary Logging (tmplog)

The intent log is almost always delayed. This improves performance,
but recent changes may disappear if the system crashes. This mode is
only recommended for temporary file systems.

4. No Logging (nolog)

The intent log is disabled. The other three logging modes provide for
fast file system recovery; nolog does not provide fast file system
recovery. With nolog mode, a full structural check must be
performed after a crash; this may result in loss of substantial portions
of the file system, depending upon activity at the time of the crash.
Usually, a nolog file system should be rebuilt with mkfs(1M) after a
crash. The nolog mode should only be used for memory resident or
very temporary file systems.


Regards
Animesh

[Insu Kim]

Some system calls return before the intent log is written,
Improves performances but structural changes are not immediately guaranteed.
Recent changes may be lost if a system failure occures.

Something about intent log :

1. JFS maintains information on imcomplete metadata changes in an intent log.
2. Full file system structural recovery available if intent log is corrupted.
3. intent log is written synchronously before metadata is changed.

Hope this helps,

[Marcin Wicinski]

Hi, should help:

-o delaylog ??? Intent log writes are asynchronous. ???Double??? write
will still occur but the process does not block while the intent log is being
written to ?? potential performance increase.

-o tmplog ??? Intent log writes are delayed; recent changed will be lost
if the system crashes. This option is recommended for temporary file systems.


-o mincache=direct ??? All reads and non O_SYNC writes are
unbuffered. This degrades performance. The trade-off is to reduce the need for
pages in buffer cache versus process blocking. Use for large I/O direct from
the application.


-o mincache=tmpcache ??? Disable delayed writes and extent clears when
file is extended; explicit fsync required to post changes. The trade-off is
data integrity versus performance. This option is useful for temporary
files.


-o convosync=direct ??? Converts reads and O_SYNC writes to
unbuffered. Improve the performance. The trade-off is between increased
performances when source code is not available versus possible loss of data
integrity.


-o nodatainlog ??? Posts O_SYNC writes of the data directly to the
file. Improve performance. The trade-off is a fewer writes with possibly
increased head movement versus double writes with less head moves.