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NAMElvm — Logical Volume Manager (LVM) DESCRIPTIONThe 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 raw access. CommandsLVM information can be created, displayed, and manipulated
with the following commands:
- 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 volume - 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 group - lvrmboot
Remove logical volume link to root, primary swap, or dump volume - pvchange
Change characteristics of physical volume in volume group - 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 backup file - 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 logical volumes - vgextend
Extend an volume group by adding physical volumes - 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 volumes - lvsync
Synchronize stale mirrors in logical volumes - vgsync
Synchronize stale logical volume mirrors in volume groups
EXAMPLESThe 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 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.
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.
lvdisplay /dev/vg01/lvol1 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
SEE ALSOlvchange(1M),
lvcreate(1M),
lvdisplay(1M),
lvextend(1M),
lvlnboot(1M),
lvreduce(1M),
lvremove(1M),
lvrmboot(1M),
pvchange(1M),
pvcreate(1M),
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),
lvsync(1M),
vgsync(1M). If HP ServiceGuard is installed:
cmcheckconf(1M),
cmquerycl(1M),
Managing MC/ServiceGuard. |
