Xfs - Novell LINUX ENTERPRISE SERVER 11 - STORAGE ADMINISTRATION GUIDE 2-23-2010 Administration Manual

Better Disk Space Utilization
In ReiserFS, all data is organized in a structure called a B*-balanced tree. The tree structure
contributes to better disk space utilization because small files can be stored directly in the B* tree
leaf nodes instead of being stored elsewhere and just maintaining a pointer to the actual disk
location. In addition to that, storage is not allocated in chunks of 1 or 4 KB, but in portions of the
exact size needed. Another benefit lies in the dynamic allocation of inodes. This keeps the file
system more flexible than traditional file systems, like Ext2, where the inode density must be
specified at file system creation time.
Better Disk Access Performance
For small files, file data and "stat_data" (inode) information are often stored next to each other. They
can be read with a single disk I/O operation, meaning that only one access to disk is required to
retrieve all the information needed.
Fast Crash Recovery
Using a journal to keep track of recent metadata changes makes a file system check a matter of
seconds, even for huge file systems.
Reliability through Data Journaling
ReiserFS also supports data journaling and ordered data modes similar to the concepts outlined in
"Ext3" on page 15. The default mode is
integrity, but uses journaling only for metadata.

1.2.5 XFS

Originally intended as the file system for their IRIX OS, SGI started XFS development in the early
1990s. The idea behind XFS was to create a high-performance 64-bit journaling file system to meet
extreme computing challenges. XFS is very good at manipulating large files and performs well on
high-end hardware. However, even XFS has a drawback. Like ReiserFS, XFS takes great care of
metadata integrity, but less care of data integrity.
A quick review of XFS's key features explains why it might prove to be a strong competitor for
other journaling file systems in high-end computing.
"High Scalability through the Use of Allocation Groups" on page 17
"High Performance through Efficient Management of Disk Space" on page 18
"Preallocation to Avoid File System Fragmentation" on page 18
High Scalability through the Use of Allocation Groups
At the creation time of an XFS file system, the block device underlying the file system is divided
into eight or more linear regions of equal size. Those are referred to as allocation groups. Each
allocation group manages its own inodes and free disk space. Practically, allocation groups can be
seen as file systems in a file system. Because allocation groups are rather independent of each other,
more than one of them can be addressed by the kernel simultaneously. This feature is the key to
XFS's great scalability. Naturally, the concept of independent allocation groups suits the needs of
multiprocessor systems.
, which ensures both data and metadata
data=ordered
Overview of File Systems in Linux 17