
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.
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:
•
For volume group Version 1.0 or 2.0,
lvchange
,
lvcreate
,
lvextend
,
lvmerge
,
lvmove
,
lvreduce
,
lvremove
,
lvsplit
,
vgextend
,
vgmodify
,
vgmove
, and
vgreduce
cannot
be used in shared mode.
•
The
pvmove
command cannot be used in shared mode for volume group Version 1.0.
•
For
pvchange
, only the
-a
option (for attaching or detaching a path to the specified physical
volume) is allowed in shared mode. All other
pvchange
options are not supported in shared
mode.
To replace disks that are part of a volume group shared by a Serviceguard cluster, the physical
volume must be detached and attached (using
pvchange
) independently on each of the
systems in the cluster.
•
The
lvlnboot
and
lvrmboot
commands cannot be used in shared mode.
18
Introduction