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xfs(4)									xfs(4)

NAME    [Toc]    [Back]

     xfs - layout of the XFS filesystem

DESCRIPTION    [Toc]    [Back]

     An	XFS filesystem can reside on a regular disk partition or on a logical
     volume (see l
).  An XFS filesystem has up	to three
     parts:  a data section, a log section, and	a real-time section.  For disk
     partition and lv logical volume filesystems, the real-time	section	is
     absent, and the log area is contained within the data section.  For XLV
     logical volume filesystems, the real-time section is optional, and	the
     log section can be	separate from the data section or contained within it.
     The filesystem sections are divided into a	certain	number of blocks,
     whose size	is specified at	mkfs(1M) time with the -b option.

     The data section contains all the filesystem metadata (inodes,
     directories, indirect blocks) as well as the user file data for ordinary
     (non-real-time) files and the log area if the log is internal to the data
     section.  The data	section	is divided into	a number of allocation groups.
     The number	and size of the	allocation groups are chosen by	mkfs so	that
     there is normally a small number of equal-sized groups.  The number of
     allocation	groups controls	the amount of parallelism available in file
     and block allocation.  It should be increased from	the default if there
     is	sufficient memory and a	lot of allocation activity.  The number	of
     allocation	groups should not be set very high, since this can cause large
     amounts of	CPU time to be used by the filesystem, especially when the
     filesystem	is nearly full.	 More allocation groups	are added (of the
     original size) when xfs_growfs(1M)	is run.

     The log section (or area, if it is	internal to the	data section) is used
     to	store changes to filesystem metadata while the filesystem is running
     until those changes are made to the data section.	It is written
     sequentially during normal	operation and read only	during mount.  When
     mounting a	filesystem after a crash, the log is read to complete
     operations	that were in progress at the time of the crash.

     The real-time section is used to store the	data of	real-time files.
     These files had an	attribute bit set through fcntl(2) after file
     creation, before any data was written to the file.	 The real-time section
     is	divided	into a number of extents of fixed size (specified at mkfs
     time).  Each file in the real-time	section	has an extent size that	is a
     multiple of the real-time section extent size.

     Each allocation group contains several data structures.  The first	sector
     contains the superblock.  For allocation groups after the first, the
     superblock	is just	a copy and is not updated after	mkfs.  The next	three
     sectors contain information for block and inode allocation	within the
     allocation	group.	Also contained within each allocation group are	data
     structures	to locate free blocks and inodes; these	are located through
     the header	structures.

									Page 1

xfs(4)									xfs(4)

     Each XFS filesystem is labeled with a unique universal identifier (UUID).
     (See uuid(3C) for more details.)  The UUID	is stored in every allocation
     group header and is used to help distinguish one XFS filesystem from
     another, therefore	you should avoid using dd or other block-by-block
     copying programs to copy XFS filesystems.	If two XFS filesystems on the
     same machine have the UUID, xfsdump may become confused when doing
     incremental and resumed dumps.  (See xfsdump(1M) for more details.)
     xfs_copy or xfsdump/xfsrestore are	recommended for	making copies of XFS

     All these data structures are subject to change, and the headers that
     specify their layout on disk are not provided.

SEE ALSO    [Toc]    [Back]

     attr(1), grio(1M),	mkfs(1M), mkfs_xfs(1M),	xfs_bmap(1M), xfs_check(1M),
     xfs_copy(1M), xfs_estimate(1M), xfs_growfs(1M), xfs_logprint(1M),
     xfs_repair(1M), xfsdump(1M), xfsrestore(1M), fcntl(2), syssgi(2),
     uuid(3C), filesystems(4), lv(7M), xlv(7M).

									Page 2

filesystems(4)							filesystems(4)

NAME    [Toc]    [Back]

     filesystems: cdfs,	dos, fat, EFS, hfs, mac, iso9660, cd-rom, kfs, nfs,
     XFS, rockridge - IRIX filesystem types

DESCRIPTION    [Toc]    [Back]

     IRIX supports a number of different filesystems.  Some of these types are
     names that	can be used with the mount(1) command's	-t option.  Others are
     just common names and cannot be used with the mount command.  An example
     of	this is	the RockRidge type, which is a superset	of the iso9660
     filesystem	type.  Therefore RockRidge filesystems are mounted with	a
     command similar to	this:

	  mount	-t iso9660 -o ro /dev/rdsk/dks0d3vol /CDROM

     The following filesystem types are	supported:

     bds	 Not a file system type, an extension to NFS for bulk data
		 transfers.  The BDSpro	server is an optional product and must
		 be purchased separately.

     cdfs (CD-ROM)
		 Same as type iso9660 (see below); this	is the ABI compliant

     dos (fat)	 The filesystem	used by	many personal computers.  Types	1, 4,
		 and 6 are supported, included long names where	supported.
		 Type 5	(extended partitions) are supported only if mounted
		 with the partition # options.	IRIX support for dos
		 filesystems is	restricted to removable	disk devices such as
		 floppy	and floptical disks.  Filenames	on dos filesystems are
		 restricted to up to an	eight character	name followed by an
		 optional period and three character filename extension, for
		 most types.  Longer names are supported to a limited degree,
		 on the	types where the	native OS supports them.

     EFS	 The older extent-based	disk filesystem	used by	IRIX for disks
		 and also for IRIX software distribution CD-ROMs.  See efs(4)
		 for more details.

     fd		 A filesystem used to access process file descriptors.

     hfs (mac)	 The filesystem	used by	Macintosh computers.  IRIX support for
		 hfs filesystems is restricted to removable disk devices such
		 as floppy and floptical disks and to CD-ROMs.	A hfs file is
		 composed of three portions:  a	data fork, a resource fork,
		 and a desktop information entry.  The data fork appears in a
		 normal	directory.  The	resource fork in a special directory
		 (.HSResource) in the file's directory.	 The desktop
		 information for all files in a	directory is contained in the
		 special file .HSancillary.

									Page 1

filesystems(4)							filesystems(4)

     iso9660 (CD-ROM)
		 A CD-ROM filesystem type conforming to	ISO standard 9660.
		 iso9660 CD-ROMs are used when the contents of the CD-ROM is
		 intended to be	readable by a variety of operating systems.
		 You must install the optional subsystem eoe.sw.cdrom to be
		 able to mount and read	an iso9660 CD-ROM.  Also see RockRidge
		 below.	 Note that IRIX	software distribution CD-ROMs are not
		 iso9660 filesystems, they are efs filesystems.	 Music CDs are
		 not file structured and are not used as filesystems.  Music
		 CDs can be played using the CD-ROM drive using	cdman(1) or

     kfs	 A network filesystem used to access disks on located on
		 remote	computers using	AppleShare networking.	Generally,
		 AppleShare networking is used to access Macintosh computers.
		 Except	for the	disk location, kfs filesystems are identical
		 to hfs	filesystems.

     nfs	 A network filesystem used to access disks located on remote
		 computers.  Both NFS Version 2, and NFS Version 3 are
		 supported.  NFS is an optional	product	and must be purchased
		 separately.  The subsystem nfs.sw.nfs must be installed to
		 use NFS.

     proc	 A filesystem that provides access to the image	of each	active
		 process in the	system.

     hwgfs	 A filesystem that provides access to the system hardware

     RockRidge	 A filesystem layered on type of the iso9660 filesystem	type
		 (see above) that provides semantics closer to those of
		 standard UNIX filesystems.  In	particular, it supplies	file
		 permissions and allows	for directory hierarchies more than 8
		 levels	deep.

     XFS	 The next-generation 64-bit high performance journaling
		 filesystem used by IRIX for disks.  See xfs(4)	for more

     cachefs	 A caching filesystem for use with efs,	xfs, nfs, nfs3,
		 iso9660, hfs, dos, kfs, and cdfs.  See	cachefs(4) for

NOTE    [Toc]    [Back]

     The nfs and kfs filesystems are optional products.	 Support for iso9660
     filesystems is in the optional subsystem eoe.sw.cdrom.

     IRIX implements dos, hfs, iso9660,	and kfs	filesystems as user mode NFS
     daemons.  In some cases errors detected by	these daemons are reported as
     NFS errors.  Although NFS is a product option, support for	these
     filesystem	types is not dependent on the installation of NFS.

									Page 2

filesystems(4)							filesystems(4)

SEE ALSO    [Toc]    [Back]

     exportfs(1M), fpck(1M), fsck(1M), mediad(1M), mkfp(1M), mkfs(1M),
     mount(1M),	mount_kfs(1M), efs(4), fd(4), fstab(4),	hwgfs(4), proc(4),

									PPPPaaaaggggeeee 3333
[ Back ]
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