lvm.7 (2010 10)

ManualsBrandsHP ManualsSoftwareHP-UX Manpages

lvm(7) lvm(7)

NAME

lvm - Logical Volume Manager (LVM)

DESCRIPTION

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 avai-

lability (with the optional HP Serviceguard software), and striping, that enhance availability and perfor-

mance. LVM also provides the snapshot feature to create point-in-time images (snapshots) of LVM logical

volumes.

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 size of an extent can vary from 1 MB to 256 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,

where as 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.

Commands

LVM 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

lvmadm Display limits associated with a volume group version

lvmove Move a logical volume within a volume group

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 a volume group and its associated logical volumes

vgextend Extend a volume group by adding physical volumes

vgimport Import a volume group onto the system

vgmodify Modify volume group attributes

vgmove Move data from old set of disks to a new set of disks

vgreduce Remove physical volumes from a volume group

vgremove Remove volume group deﬁnition from the system

vgscan Scan physical volumes for volume groups

vgversion Migrate a volume group from one volume group version to another

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

HP-UX 11i Version 3: October 2010 − 1 − Hewlett-Packard Company 1

Summary of content (6 pages)

PAGE 1
lvm(7) lvm(7) NAME lvm - Logical Volume Manager (LVM) DESCRIPTION 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. LVM also provides the snapshot feature to create point-in-time images (snapshots) of LVM logical volumes.
PAGE 2
lvm(7) lvm(7) lvsync vgsync Synchronize stale mirrors in logical volumes Synchronize stale logical volume mirrors in volume groups Device Special Files Starting with HP-UX 11i Version 3, the Mass Storage Stack supports two naming conventions for the device special 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).
PAGE 3
lvm(7) lvm(7) • Extent size is now a required parameter. For volume groups version 1.0, the default extent size is 4MB. For volume groups version 2.0 or higher, extent size must be specified. Volume group versions 2.0 and 2.1 do not support root, boot, swap, or dump. Volume group versions 2.2 and higher do support root, boot, swap, and dump. Volume groups version 2.0 or higher do not support spare physical volumes. The maximum number of 1.0 version volume groups per system is 256.
PAGE 4
lvm(7) lvm(7) The logical volume and all of its snapshots together form a snapshot tree. The logical volume of which the snapshots were taken is referred to as the "original" logical volume. Only a single snapshot can be created at a time, which means that one cannot create point-in-time copies of more than one logical volume at a time. Also, snapshots can only be created off normal logical volumes, and not off snapshot logical volumes.
PAGE 5
lvm(7) lvm(7) If an unshare operation fails on a snapshot, it gets marked as inoperative. All reads and writes on an inoperative logical volume will fail. Snapshots are by default read-only logical volumes, but the user can choose to create writable snapshots. See lvcreate (1M) and lvchange (1M) for more information. If a logical volume has snapshots associated with it, then there could be an increase in the latencies associated with reads and writes on the original logical volume or its snapshots.
PAGE 6
lvm(7) lvm(7) 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.