lvm - Logical Volume Manager (LVM)
The Logical Volume Manager (LVM) is a subsystem for managing disk
space. The HP LVM subsystem offers value-added features, such as
mirroring (with the optional HP MirrorDisk/UX software), high
availability (with the optional HP ServiceGuard software), and
striping, that enhance availability and performance.
Unlike earlier arrangements where disks were divided into fixed-sized
sections, LVM allows the user to consider the disks, also known as
physical volumes, as a pool (or volume) of data storage, consisting of
equal-sized extents. The default size of an extent is 4 MB.
An LVM system consists of arbitrary groupings of physical volumes,
organized into volume groups. A volume group can consist of one or
more physical volumes. There can be more than one volume group in the
system. Once created, the volume group, and not the disk, is the
basic unit of data storage. Thus, whereas earlier one would move
disks from one system to another, with LVM, one would move a volume
group from one system to another. For this reason it is often
convenient to have multiple volume groups on a system.
Volume groups can be subdivided into virtual disks, called logical
volumes. A logical volume can span a number of physical volumes or
represent only a portion of one physical volume. The pool of disk
space that is represented by a volume group can be apportioned into
logical volumes of various sizes. The size of a logical volume is
determined by its number of extents. Once created, logical volumes
can be treated just like disk partitions. Logical volumes can be
assigned to file systems, used as swap or dump devices, or used for
LVM information can be created, displayed, and manipulated with the
lvchange Change logical volume characteristics
lvcreate Stripe, create logical volume in volume group
lvdisplay Display information about logical volumes
lvextend Increase space, increase mirrors for logical
lvlnboot Prepare logical volume to be root, primary
swap, or dump volume
lvmmigrate Prepare root file system for migration from
partitions to logical volumes
lvreduce Decrease number of physical extents allocated
to logical volume
lvremove Remove one or more logical volumes from volume
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lvrmboot Remove logical volume link to root, primary
swap, or dump volume
pvchange Change characteristics of physical volume in
pvcreate Create physical volume for use in volume group
pvdisplay Display information about physical volumes
within volume group
pvmove Move allocated physical extents from one
physical volume to other physical volumes
vgcfgbackup Create or update volume group configuration
vgcfgrestore Display or restore volume group configuration
from backup file
vgchange Set volume group availability
vgcreate Create volume group
vgdisplay Display information about volume groups
vgexport Export an volume group and its associated
vgextend Extend an volume group by adding physical
vgimport Import an volume group onto the system
vgreduce Remove physical volumes from an volume group
vgremove Remove volume group definition from the system
vgscan Scan physical volumes for volume groups
The following commands are also available if the HP MirrorDisk/UX
software is installed:
lvmerge Merge two logical volumes into one logical volume
lvsplit Split mirrored logical volume into two logical
lvsync Synchronize stale mirrors in logical volumes
vgsync Synchronize stale logical volume mirrors in volume
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
+ Collect all the physical volumes to form a new volume group
+ Create logical volumes from the space in the volume group
+ Use each logical volume as if it were a disk section (create
a file system, or use for raw access).
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To configure disk /dev/dsk/c0t0d0 as part of a new volume group named
First, initialize the disk for LVM with the pvcreate command.
Then, create the pseudo device file that is used by the LVM
mknod /dev/vg01/group c 64 0x030000
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 09. The maximum value of NN is
controlled by the kernel tunable parameter, maxvgs.
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 command.
lvcreate -L 100 -n usrvol /dev/vg01
This creates two device files for the logical volume,
/dev/vg01/usrvol, which is the block device file, and
/dev/vg01/rusrvol, which is the character (raw) device file.
You can view information about the newly created logical volume
with the lvdisplay command.
Any operation allowed on a disk partition is allowed on the
logical volume. Thus, you can use usrvol to hold a file system.
newfs /dev/vg01/rusrvol hp7937
mount /dev/vg01/usrvol /usr
lvchange(1M), lvcreate(1M), lvdisplay(1M), lvextend(1M), lvlnboot(1M),
lvreduce(1M), lvremove(1M), lvrmboot(1M), pvchange(1M), pvcreate(1M),
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pvdisplay(1M), pvmove(1M), vgcfgbackup(1M), vgcfgrestore(1M),
vgchange(1M), vgcreate(1M), vgdisplay(1M), vgexport(1M), vgextend(1M),
vgimport(1M), vgreduce(1M), vgremove(1M), vgscan(1M).
Managing Systems and Workgroups.
If HP MirrorDisk/UX is installed: lvmerge(1M), lvsplit(1M),
If HP ServiceGuard is installed: cmcheckconf(1M), cmquerycl(1M),
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