HP-UX Reference (11i v3 07/02) - 7 Device (Special) Files, 9 General Information, Index (vol 10)

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lvm(7) lvm(7)
Device Special Files
In this release of HP-UX 11i, the Mass Storage Stack supports two naming conventions for the device spe-
cial files used to identify devices (see intro(7)). Devices can be represented using:
• Persistent device special files, (
/dev/disk/disk3
), or
• Legacy device special file names, (
/dev/dsk/c0t6d6).
While LVM supports the use of both conventions within the same volume group, the examples shown in the
LVM man pages are all using the legacy device special file convention.
Alternate Links (PVLinks)
In this release of HP-UX, LVM continues to support Alternate Links to a device to allow continued access to
the device, if the primary link fails. This multiple link or multipath solution increases data availability, but
continues disallowing the use of multiple paths simultaneously.
A new feature was introduced in the Mass Storage Subsystem on HP-UX 11i Version 3 that supports multi-
ple paths to a device and allows simultaneous access to these paths. The Mass Storage Subsystem will bal-
ance the I/O load across the valid paths. Multipathing is the default unless the
scsimgr command is used
to enable legacy multipathing and also the active path is a legacy device special file. See scsimgr(1M) for
details.
Even though the Mass Storage Subsystem supports 32 multiple paths per physical volume on this version
of HP-UX, LVM does not support more than eight paths to any physical volume. As a result, commands
like
vgcreate and vgextend will not succeed in adding more than eight paths per physical volume.
Additionally, vgimport and vgscan cannot write more than eight paths per physical volume in the
/etc/lvmtab file. If users want to use any specific path other than these eight paths, then they have to
vgreduce one of the alternate paths in the volume group and add that specific path using
vgextend.
It is no longer required or recommended to configure LVM with alternate links. However, it is possible to
maintain the traditional LVM behavior. To do so, both of the following criteria must be met:
• Only the legacy device special file naming convention is used in the volume group configuration.
• The
scsimgr command is used to enable the legacy multipath behavior for each physical volume
in the volume group.
EXAMPLES
The basic steps to take to begin using LVM are as follows:
• Identify the disks to be used for LVM.
• Create an LVM data structure on each identified disk (see pvcreate(1M)).
• Collect all the physical volumes to form a new volume group (see vgcreate (1M)).
• Create logical volumes from the space in the volume group (see lvcreate(1M)).
• Use each logical volume as if it were a disk section (create a file system, or use for raw access).
To configure disk
/dev/dsk/c0t0d0
as part of a new volume group named vg01:
First, initialize the disk for LVM with the
pvcreate command.
pvcreate /dev/rdsk/c0t0d0
Then, create the pseudo device file that is used by the LVM subsystem.
mkdir /dev/vg01
mknod /dev/vg01/group c 64 0x010000
The minor number for the group file should be unique among all the volume groups on the system. It has
the format 0xNN0000, where NN ranges from 00 to ff.
Create the volume group, vg01, containing the physical volume, /dev/dsk/c0t0d0, with the
vgcreate command.
vgcreate /dev/vg01 /dev/dsk/c0t0d0
You can view information about the newly created volume group with the vgdisplay command.
vgdisplay -v /dev/vg01
Create a logical volume of size 100 MB, named usrvol, on this volume group with the lvcreate com-
mand.
80 Hewlett-Packard Company − 2 − HP-UX 11i Version 3: February 2007