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vh(7M)									vh(7M)

NAME    [Toc]    [Back]

     vh	- disk volume header

DESCRIPTION    [Toc]    [Back]

     The volume	header is a small partition at the start of every SGI disk.
     Typically it occupies about 2 megabytes, large enough to hold files used
     to	boot the system.  Option disks typically do not	need this much space,
     but are initialized the same so that they can be easily made into system
     disks if desired.	It contains identifying	information for	the disk and
     may also contain some files used in standalone operations when the
     operating system is not running.

     The volume	header of the system root disk can be accessed as /dev/rvh.

     The volume	header partitions of other disks can be	accessed via the
     appropriate files in the /dev/rdsk	directory; the volume header special
     files are identified by the suffix	`vh'.  The block devices are not
     created by	default.  If they are created specially, they can be used

     The first sector of the volume header (and	hence the first	sector on the
     entire disk) contains the disk label.  The	structure of this is defined
     in	the file <sys/dvh.h>.  The file	is quite extensively commented,	and it
     is	worth referring	to it as a supplement to the information in this
     reference page.

     The disk label contains the following sections:

     Magic Number
	  This is a unique number which	serves to verify that the sector does
	  contain a label.

     Root Partition Identifier
	  If the disk is a system disk,	this field identifies the partition to
	  be used as the root partition.  The information was used by older
	  boot PROMs when the system was booted.  It is	redundant on all
	  current systems (those supported by this release), but is still set.
	  It is	used only if the value of the nvram variable OSLoadFilename is
	  not set (either permanently, or as derived from the other nvram

     Swap Partition Identifier
	  This information is used during system boot.

     Boot Filename
	  This information is used during system boot; it identifies the
	  executable file to be	loaded by default (normally the	operating

     Device Parameters
	  This section is no longer used for any device-specific geometry
	  information, despite it's name.  Older style disk controllers, such

									Page 1

vh(7M)									vh(7M)

	  as ESDI and SMD that required	it are no longer supported.  Currently
	  only the queuing depth to be used for	each disk drive	is read	by the
	  disk driver from this	structure.

     Volume Directory
	  As well as the label,	the volume header partition can	store files in
	  the remaining	space.	These are NOT regular system files; they are
	  accessed only	via the	PROM or	standalone shell and do	not need to
	  appear in any	regular	directory.  They are typically installed in
	  the volume header when the operating system is installed.

	  The Volume Directory is a table in the disk label which enables such
	  files	to be located by the PROMs.  Files in the volume header	can be
	  added	or removed by dvhtool(1M).  Filenames may be from 1 to 8
	  characters long.

	  Disk space is	required for a number of different purposes in a
	  system.  It is not usually practical or desirable to dedicate	an
	  entire physical disk to each use, so the disk	surface	is divided
	  into a number	of partitions.	Typically a partition contains a
	  filesystem (such as /usr) or is used for non-filesystem storage,
	  such as swap.	 The volume header itself is also a partition.
	  Partitions can overlap:  for example,	the vol	partition is defined
	  to be	the whole disk (useful for disk	cloning).

	  In order to direct I/O requests to the correct part of the disk, the
	  driver must know the layout of the partitions.  This is specified in
	  the partition	table contained	in the disk label.

     The disk label is created by fx when the disk is first initialized.  A
     convenient	summary	of its contents	can be printed by prtvtoc(1M).

FILES    [Toc]    [Back]


SEE ALSO    [Toc]    [Back]

     dvhtool(1M), fx(1M), prtvtoc(1M).

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 Similar pages
Name OS Title
prtvtoc IRIX print disk volume header information
dvhtool IRIX modify and obtain disk volume header information
lifinit HP-UX write LIF volume header on file
vxres_lvmroot HP-UX restore LVM root disk from VERITAS Volume Manager root disk
vxcp_lvmroot HP-UX copy LVM root disk onto new VERITAS Volume Manager root disk
xlv IRIX logical volume disk driver
vxdestroy_lvmroot HP-UX remove LVM root disk and associated LVM volume group
vxdisksetup HP-UX configure a disk for use with VERITAS Volume Manager
vxdmp HP-UX VERITAS Volume Manager multipathing disk devices
xlv_assemble IRIX initialize logical volume objects from disk labels
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