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Tuning ext3 PDF Print E-mail
Written by Schelstraete Bart   
Tuesday, 02 June 2009 20:05
This is a 5 seconds commit interval in EXT3, which is the standard behaviour. You can check this in your syslog.
here the ext3.txt from the kernel documentation (<kernel dir>/Documentation/filesystems/ext3.txt:
Quote:
(...)commit=nrsec
Ext3 can be told to sync all its data and metadata
every 'nrsec' seconds. The default value is 5 seconds.
This means that if you lose your power, you will lose
as much as the latest 5 seconds of work (your
filesystem will not be damaged though, thanks to the
journaling). This default value (or any low value)
will hurt performance, but it's good for data-safety.
Setting it to 0 will have the same effect as leaving
it at the default (5 seconds).
Setting it to very large values will improve
performance.

(in the following mini-HOWTO are added more performance options, if you don't want them then only add the "commit=seconds" option (in the same order though)

1st step
Take your /etc/fstab and add these options for your /root (and/or /home etc) partition:
Code:
(previous options...),noatime,nodiratime,nobh,data=writeback,commit=100
I guess you will also be very happy with the "data=writeback" and "nobh" option. This works for ext3. I guess for reiser also, but please check this before..

2nd step
To make data=writeback and the new commit interval work get your /boot/grub/menu.lst
See the "defoptions=" line and add (e.g. after "ro quiet splash") -->
Code:
quiet splash rootflags=data=writeback,nobh,commit=100
also add (only) "rootflags=data=writeback" to the altoptions=-line!

Then
Code:
sudo update-grub
3rd step
For data=writeback, the last step before rebooting is (works with mounted filesystem )
Code:
sudo tune2fs -o journal_data_writeback /dev/hd(...)
For all your partitions, e.g. if you have /root and /home seperated.

finally...
Then do a reboot. However, the specific option you were looking for is the "commit=sec" options. The value is measured is seconds.

caution!
I had several crashes (not linux' fault ) and my data is still there, although these options increases a possible risk of data loss!!! Note: You are not disabling journaling with this. so it's still pretty safe. (however, own risk)


Appendix
PS: My posting seems quite confusing, I guess. So here are the specific example lines/files:

/etc/fstab:
Code:
/dev/hdc2    /   ext3   defaults,errors=remount-ro,data=writeback,noatime,nodiratime,nobh,commit=100     0     1
(do the same for if you have a seperated /home)

/boot/grub/menu.lst
Code:
(...)
## additional options to use with the default boot option, but not with the
## alternatives
## e.g. defoptions=vga=791 resume=/dev/hda5
# defoptions=quiet splash rootflags=data=writeback,nobh,commit=100
(...)
## altoption boot targets option
## multiple altoptions lines are allowed
## e.g. altoptions=(extra menu suffix) extra boot options
##      altoptions=(recovery) single
# altoptions=(recovery mode) single rootflags=data=writeback
####for the alt options only the data=writeback options is necessary
(...)
don't forget to run a "sudo update-grub"!

Be sure, to have e.g. a live cd to access the system if you make at typing error or so in one of these config files.

WARNING (again) of possible several data loss. Do at your own risk.
This is recommended for laptops and/or desktop systems. Don't do this on servers!

DON'T MAKE A TYPING ERROR BY MIXING UP tune2fs with mke2fs!!! This happened once to me and will erase all your data.

more information
Kernel-Documentation (mostly <directories to kernel>/Documentation/filesytems/ext3.txt
very interesting

manpages: tune2fs
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