HP-UX System Administrator's Guide: Logical Volume Management (762803-001, March 2014)

A smaller-than-default extent size or number of physical extents might be preferable. A high-capacity
physical volume might be unusable in a volume group whose extent size is small or set with a small
number of physical extents per disk.
1.6.5 User Data Area
The user data area is the region of the LVM disk used to store all user data, including file systems,
virtual memory system (swap), or user applications.
1.7 LVM Limitations
LVM is a sophisticated subsystem. It requires time to learn, it requires maintenance, and in rare
cases, things can go wrong.
HP recommends using logical volumes as the preferred method for managing disks. Use LVM on
file and application servers. On servers that have only a single disk and are used only to store the
operating system and for swap, a “whole-disk” approach is simpler and easier to manage. LVM
is not necessary on such systems.
By default, LVM configurations are automatically backed up each time you change them, in the
default directory, /etc/lvmconf. Mirroring provides insurance against data loss that is not
available under the whole-disk method.
NOTE: This default directory /etc/lvmconf can be changed for volume groups Version 2.x
by configuring a new path in the LVMP_CONF_PATH_NON_BOOT variable defined in the /etc/
lvmrc file. See vgcfgbackup(1M) for details.
Additional limitations to LVM include the following:
• Both LVM disks and non-LVM disks can exist simultaneously on your system, but a given disk
or partition must be managed entirely by either LVM or non-LVM methods. That is, you cannot
combine these techniques for use with a single disk or partition.
• On an HP Integrity server, LVM supports partitioning of the root disk and its mirrors only, and
supports only one HP-UX partition on any disk.
• Floppy disks, optical disks, and CD-ROMs do not support logical volumes.
• You must use an LVM or VERITAS™ Volume Manager (VxVM) disk for your root disk.
• To use LVM, a disk must be first initialized into a physical volume.
• To be allocatable for storage, a physical volume must be assigned to a volume group.
• A physical volume can belong to only one volume group.
• The extent size of a volume group is fixed when the volume group is created. It cannot be
changed without recreating the volume group.
1.8 Shared LVM
Shared LVM (SLVM) allows multiple systems in a Serviceguard cluster to share (read/write) disk
resources in the form of volume groups. SLVM is designed to be used by specialized distributed
applications that use raw access to disks, rather than going through a file system.
Shared mode is configured with the vgchange command. The vgdisplay command will show
the current activation mode for the volume group.
The following commands have restrictions when operated on volume groups that are activated in
shared mode:
1.7 LVM Limitations 21