24 Linux for IBM ^ zSeries and S/390: Distributions
Here we see that a packet size of 4096 bytes takes about twice as long to get to
another machine, but there are no MTU size problems. If there had been
problems, the ping would have timed out.
2.3 Planning for Linux distribution and software
While planning for hardware might seem challenging, planning a Linux
distribution and any additional software to be added and configured is probably
harder. The remainder of this redbook is devoted to covering these topics.
In this section we offer a general discussion on file systems.
2.3.1 Planning file systems
The term file systems is used to refer to a few different concepts. Let us classify
file systems into:
򐂰 Conventional
򐂰 Journaled
򐂰 Virtual
򐂰 Swap
Conventional file systems
Conventional file systems are limited. They can only be contained on a single raw
device, and the file size is limited by the device size. An example of a
conventional file system (and the most commonly used file system in Linux) is
To check and repair a conventional file system, the command fsck must be run
against it. With small partitions, this process is reasonable; however, with large
partitions, it can become prohibitively slow. Therefore, a more sophisticated file
system must be used.
Journaled file systems
A journaled file system is one in which changes are recorded or journaled. Most
modern UNIX operating systems use journaled file systems, and Linux is
certainly moving in that direction. However, while the conventional second
extended file system (ext2) is clearly the de facto standard on Linux, there is no
such standard with journaled file systems. We investigated the Reiser file system
(reiserfs) and the IBM Journaled File System (JFS).
Chapter 2. Planning for Linux 25
The Reiser file system
The Reiser file system (reiserfs) is one of the most well-known journaling file
systems that works on Linux. Unfortunately, during the residency we discovered
that the official source tree does not contain support for big-endian architectures
such as the S/390, POWERpc, etc. (Big-endian architectures store the four bytes
of an address in the same order, lowest to highest, as the network byte order, or
that which is sent across the network. With little-endian architectures, such as
Intel, the lowest memory address contains the low order byte, and the order must
be reversed to be sent over the network.)
Jeff Mahoney has written patches to reiserfs to make it endian safe. These
patches have not yet been merged into the official source tree. Until that time, we
cannot recommend the use of reiserfs on Linux. More information, including the
endian-safe utilities, can be found at:
The IBM Journaled File System (JFS)
JFS is the journaling file system from IBMs AIX operating system. It was made
open source sometime last year and IBM started a project to port it to Linux. Beta
1 was released in December 2000, Beta 2 in March 2001, and Beta 3 in April
2001. The first release of the JFS was made available on June 28, 2001. The
project team workign on porting to Linux has focused its efforts on the 2.4 kernel,
although patches can be found for the 2.2.x version of the Linux kernel. Version
1.0.0 of the JFS can be found at:
See 18.7, Using journaled file systems on page 343 for details on using this file
Virtual file systems
Virtual file systems are those which are not actually written to disk. The prime
example of a virtual file system is the /proc file system. It contains data structures
used by the kernel and is available to the user via this file system.
Another virtual file system, the /dev file system, has been added to the Linux 2.4
Swap file systems
Setting the size of a swap file can cause vigorous debates, because there is no
one right answer. Less is sometimes more because Linux will use swap space
aggressively, and keeping the memory size of Linux images small on Linux for
S/390 is important.

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