introduction to xfs

8/4/2019 Introduction to XFS

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Jonathan Wheeler

E-Science Centre, RAL

Introduction to XFS

HEPSYSMAN

5th December 2005


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e-Science Centre, RAL

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 OSs Devices are also presented in the filesystem

Linux uses virtual filesystems, e.g. /proc


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A little bit of background

Three generation of UNIX filesystems:

a) v7 / sysv / coherent / minix

b) ffs / ext2

c) vxfs / ext3 / jfs / xfs / reiserfs


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Features of 3rd generation UNIXfilesystems

a) Intent logging / journalingb) Flexible metadata structures

c) Dynamic inode allocations

d) Extents


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History of XFS

Developed by Silicon Graphics (now SGI)for use on IRIX:

1993 - original design 1994 - available for IRIX v 5.3

2000 - released as Open Source

2001/2002 some Linux distributions withnative XFS support

2003 XFS support in 2.4 kernel


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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


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XFS Features (2)

64-bit file system:a) 64bit variables for global counters and disk addresses

b) Large theoretical maximum filesystem sizei. For Linux 2.4: 2 Terabytes.

ii. For Linux 2.6 (when using 64 bit addressing on a64 bit platform): 9 Petabytes (or the device limits)

iii. For Linux 2.6 (on 32 bit platforms): 16Terabytes(even with 64 bit addressing)

c) Maximum file size is same as filesystem size


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XFS Features (3)

Partitioned into Allocation Groups:

a) each AG manages its own free space

and inodes

b) provides scalability and parallelism within

the file system

c) limits the size of the structures needed totrack this information


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XFS Features (3, continued)

d) allows many internal pointers to be 32-

bits

e) AGs typically range in size from 0.5 to4GB

f) files and directories are not limited to a

single AG.


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XFS Features (4)

Sophisticated support utilities:

a) fast mkfs (make a file system)

b) dump and restore utilities for backupc) xfsrepair to fix corrupt filesystem

d) xfs_fsr (XFS defragmenter)

e) xfsdb (XFS debug)f) xfscheck (XFS check)

g) xfs_growfs (enlarges filesystems online)


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Why you might want to use XFS

a) Stable, mature code base (oldestjournaling filesystem available on Unix)

b) Very good performance for large readsor writes

c) Designed for large systems

d) Supports user and group quotase) Support for Access Control Lists andExtended Attributes


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Extended Attributes

An extended attribute is a name/value pair

associated with a file. Attributes can be

attached to all types of inodes: regularfiles, directories, symbolic links, device

nodes, and so forth. Attribute values can

contain up to 64KB of arbitrary binarydata.

See man attr for more details


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Extended attribute namespaces

XFS implements three attribute namespaces:

a) user namespace available to all users,

protected by the normal file permissionsb) system namespace, accessible only toprivileged users and used for protectedfilesystem meta-data such as accesscontrol lists (ACLs) and hierarchical storagemanager (HSM) file migration status

c) security namespace used by securitymodules (SELinux)


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Why you might not want to use XFS

a) No data journaling

b) tar, cpio do not understand Extended

Attributes


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Resources

XFS/Linux homepage:

http://oss.sgi.com/projects/xfs/ contains

pointers to whitepapers, books, articles,etc.

Public mailing list: [email protected]

with searchable list archiveSGI Bugzilla database to report any bugs in

XFS for Linux


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Comparison tests - 1

Tests were performed:

on the same filesystem on the same

hardware (AMD Athlon 1666 Mhz, 500Mb) using 3 different operating systems:

i. Redhat 7.3 (2.4.20-28.7)

ii. Scientific Linux version 3 (2.4.21-20.EL)

iii. Scientific Linux version 4

(2.6.9-22.0.1.EL and 2.6.9.-11.EL.XFS)


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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 )


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Tests were performed:

using bonnie++ test program (see

http://www.coker.com.au/bonnie++) using the same parameters for each test:

/usr/local/sbin/bonnie++ -d /data \

-s 4096M:1024k \-n 192:1048576:128:1024 -m csfnfs30 \

-u root 1>> outputfile 2>&1


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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


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The other 6 tests measure performance for

many small files using:

Sequential create, read and delete

Random create, read and delete


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Comparsion of filesystems (Sequential output)

e t e t l e t l e t l e t l e t l l ecial

Filesystem type

Percharacter(Kb/sec)

Serie


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Comparison of filesystems (Sequential output)


Filesystem type

Perblock(Kb/sec)

Serie


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Comparison of filesystems (Sequential output


Filesystem type

Rewrite(Kb/sec)

Serie


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Comparsion of filesystems (Sequential input)


Filesystem type

Percharacter(Kb/sec)

Serie


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Comparison of filesystems (Sequential input)


Filesystem type

Perblock(Kb/sec)

Serie


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Compariosn of filesystems (Random seeks)


Filesystem type

Number/sec

Serie


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Comparison of filesystems (Sequential create)


Filesystem type

Create(Num/sec)

Serie


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Comparison of filesystems (Sequential create


Filesystem type

Read(number/sec)

Serie


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Comparison of filesystems


Filesystem type

Delete(number/sec)

Serie


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Comparison of filesystems (Random create)


Filesystem type

Create(Number/sec)

Serie


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Filesystem type

Read(Number/sec)

Serie


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Filesystem type

Delete(Number/sec)

Serie

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