1. Introduction to XFS
HEPSYSMAN
5th December 2005

2. What exactly is a filesystem ?
Organization:
Large disk space to store small data items
Use files and directories
In UNIX everything is a stream of bytes:
More complex file definition in other OS’s
Devices are also presented in the filesystem
Linux uses virtual filesystems, e.g. /proc

3. A little bit of background
Three generation of UNIX filesystems:
v7 / sysv / coherent / minix
ffs / ext2
vxfs / ext3 / jfs / xfs / reiserfs

4. Features of 3rd generation UNIX filesystems
Intent logging / journaling
Flexible metadata structures
Dynamic inode allocations
Extents

5. History of XFS
Developed by Silicon Graphics (now SGI) for use on IRIX:
original design
available for IRIX v 5.3
released as Open Source
2001/2002 – some Linux distributions with native XFS support
2003 – XFS support in 2.4 kernel

6. XFS features (1) Journaling:
but only metadata updates, not data updates.
Fast Transactions:
uses efficient B+ tree structures for fast searches and rapid space allocation

7. XFS Features (2) 64-bit file system:
64bit variables for global counters and disk addresses
Large theoretical maximum filesystem size
For Linux 2.4: 2 Terabytes.
For Linux 2.6 (when using 64 bit addressing on a 64 bit platform): 9 Petabytes (or the device limits)
For Linux 2.6 (on 32 bit platforms): 16Terabytes (even with 64 bit addressing)
Maximum file size is same as filesystem size

8. XFS Features (3) Partitioned into Allocation Groups:
each AG manages its own free space and inodes
provides scalability and parallelism within the file system
limits the size of the structures needed to track this information

9. XFS Features (3, continued)
allows many internal pointers to be 32-bits
AGs typically range in size from 0.5 to 4GB
files and directories are not limited to a single AG.

10. XFS Features (4) Sophisticated support utilities:
fast mkfs (make a file system)
dump and restore utilities for backup
xfsrepair to fix corrupt filesystem
xfs_fsr (XFS defragmenter)
xfsdb (XFS debug)
xfscheck (XFS check)
xfs_growfs (enlarges filesystems online)

11. Why you might want to use XFS
Stable, mature code base (oldest journaling filesystem available on Unix)
Very good performance for large reads or writes
Designed for large systems
Supports user and group quotas
Support for Access Control Lists and Extended Attributes

12. Extended Attributes
An extended attribute is a name/value pair associated with a file. Attributes can be attached to all types of inodes: regular files, directories, symbolic links, device nodes, and so forth. Attribute values can contain up to 64KB of arbitrary binary data.
See man attr for more details

13. Extended attribute namespaces
XFS implements three attribute namespaces:
user namespace available to all users, protected by the normal file permissions
system namespace, accessible only to privileged users and used for protected filesystem meta-data such as access control lists (ACLs) and hierarchical storage manager (HSM) file migration status
security namespace used by security modules (SELinux)

14. Why you might not want to use XFS
No data journaling
tar, cpio do not understand Extended Attributes

15. Resources
XFS/Linux homepage: contains pointers to whitepapers, books, articles, etc.
Public mailing list: with searchable list archive
SGI Bugzilla database to report any bugs in XFS for Linux

16. Comparison tests - 1 Tests were performed:
on the same filesystem on the same hardware (AMD Athlon 1666 Mhz, 500Mb)
using 3 different operating systems:
Redhat 7.3 ( )
Scientific Linux version 3 ( EL)
Scientific Linux version 4
( EL and EL.XFS)

17. Comparison tests - 2 Tests used different filesystem types:
RH 7.3 – ext2, ext3 (xfs not available)
SL 3 – ext2, ext3 (attempts to create xfs filesystem caused system crash requiring hardware reset)
SL 4 – ext2, ext3, xfs (default), xfs (custom: mkfs.xfs –d agsize=4g –i version=1 –I size=512 <device>)

18. Comparison tests - 3 Tests were performed:
using bonnie++ test program (see
using the same parameters for each test:
/usr/local/sbin/bonnie++ -d /data \
-s 4096M:1024k \
-n 192: :128:1024 -m csfnfs30 \
-u root 1>> outputfile 2>&1

19. Comparison tests - 4
12 tests in total, each reporting filesystem performance and CPU use
The first 6 tests measure I/O intensive work:
Sequential output for character, blocked and rewrites
Sequential input for character and blocked
Random seeks

20. Comparison tests - 6
The other 6 tests measure performance for many small files using:
Sequential create, read and delete
Random create, read and delete