IBM TotalStorage DS6000 Series: Performance Monitoring and Tuning

Chapter 8. Open system servers - Linux for xSeries 279

– data=writeback: This limits the data integrity guarantees, allowing old data to show up

in files after a crash. However, under some circumstances, this will increase the

performance of your disks.

– data=ordered (default mode): This guarantees that data is consistent with the file

system.

– data=journal: This requires a larger journal for a reasonable speed. It takes longer to

recover in case of an unclean shutdown, but is sometimes faster for certain database

operations.

To change the mode, add one of the following lines to the mount options for that volume in

/etc/fstab:

data=writeback

data=ordered

data=journal

For more information about ext3, see:

http://www.symonds.net/~rajesh/howto/ext3/index.html

http://ext2.sourceforge.net/2005-ols/paper-html

If maximum performance is needed, use ext2 since it has generally less overhead than any

journaling file system. But keep in mind that your data may be inconsistent in the event of a

power failure or an unclean shutdown.

ReiserFS: the default SUSE LINUX file system

The default file system on a SuSE installation since SUSE LINUX 7.1 has been ReiserFS,

developed by Hans Reiser. From its initial design, key performance aspects have included:

򐂰 Journaling designed into the file system from the beginning to improve reliability and

recovery.

򐂰 Faster access through the use of balanced tree data structures that allow for storing both

content data and security metadata.

򐂰 Efficient use of disk space because, unlike other file systems, this file system does not rely

on block sizes.

The current version of ReiserFS that is installed with SUSE LINUX Enterprise Server 8 is

V3.6. There is work underway to deliver the next release, Reiser4. The new Reiser4 file

system is expected to deliver an unbreakable file system by eliminating corruption with the

implementation of an

atomic file system where I/O is guaranteed to complete, a 2x to 5x

speed improvement by implementing new access algorithms, and ease of third-party

upgrades without reformatting, through the use of plug-ins.

8.2.8 Tuning TCP window size

You will most likely want to modify the TCP window size and use window scaling if your server

is connected to a network with high latency such as the Internet. You can either modify the

parameters on a running system by modifying values in /proc/sys/net/core/ and

/proc/sys/net/ipv4/ or modify the parameters permanently by changing values in the Linux

kernel sources and compiling your own kernel. We describe both methods in this section.

Testing performed with FTP transmissions has shown that with scalable window support

enabled and the TCP window size set to an appropriate level (depending on the network),

network throughput improves 100–500 percent on WAN links. There is less impact on

Note: ReiserFS is not supported by Red Hat Enterprise Linux AS.