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 | NOTE: This information applies only to disks belonging
to Version 1.0 volume groups. |
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There are two kinds of LVM disk layouts, one for
boot disks and another for all other LVM disks. These differ in their
data structures. Nonbootable disks have two reserved areas: the physical
volume reserved area (PVRA) and the volume group reserved area (VGRA).
Bootable disks have a PVRA and VGRA, and additional sectors reserved
for the boot data reserved area (BDRA) and boot LIF.
Boot Data Reserved Area |
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The BDRA contains the information needed to configure
the root, primary swap, and dump logical volumes, and to mount the
root file system.
Information about the LVM disk data structures
in the BDRA is maintained with the lvlnboot and lvrmboot commands. The following is a sample output:
# lvlnboot -v
Boot Definitions for Volume Group /dev/vg00:
Physical Volumes belonging in Root Volume Group:
/dev/dsk/c3t0d0 -- Boot Disk
/dev/dsk/c4t0d0 -- Boot Disk
/dev/dsk/c5t0d0
/dev/dsk/c12t0d0 -- Boot Disk
Root: lvol1 on: /dev/dsk/c3t0d0
/dev/dsk/c4t0d0
Swap: lvol2 on: /dev/dsk/c3t0d0
/dev/dsk/c4t0d0
Dump: lvol2 on: /dev/dsk/c3t0d0 |
The physical volumes designated "Boot Disk" are
bootable, having been initialized with mkboot and pvcreate -B. Multiple lines for lvol1 and lvol2 indicate that the root and swap logical
volumes are being mirrored.
Logical Interface Format Area |
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LVM boot disks contain a Logical Interface Format
(LIF) area, in which is stored a LABEL file.
On HP 9000 servers, the LIF area contains boot utilities such as the
initial system loader (ISL), the kernel boot loader
(HPUX), the autoboot file (AUTO), and offline diagnostics.
The LABEL file is created
and maintained by lvlnboot and lvrmboot. It contains information about the starting point and size of boot-relevant
logical volumes, including the boot file system (/stand). Utilities can use the LABEL file to access
the root, primary swap, and dump logical volumes without actually
using LVM.
Physical Volume Reserved Area |
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The physical volume reserved area (PVRA) contains
information describing the physical volume, such as its unique identifier,
physical extent information, and pointers to other LVM structures
on the disk.
Volume Group Reserved Area |
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The volume group reserved area (VGRA) describes
the volume group to which the disk belongs. The information is replicated
on all of the physical volumes and updated whenever a configuration
change is made. Among other data, it contains the following information:
A list of physical volumes
in the volume group, including physical volume status and size, and
a map of physical extents to logical volumes.
A list of logical volumes
in the volume group (including the status and capabilities of each
logical volume), its scheduling and allocation policies, and the number
of mirror copies.
A volume group header
containing the VGID and three configurable parameters:
the number of physical volumes allowed in the volume
group
the maximum number of logical volumes allowed in the
volume group
the maximum number of physical extents allowed per
physical volume
Since each physical extent is recorded in the
VGRA, the extent size has a direct bearing on the size of the VGRA.
In most cases, the default extent size is sufficient. However, if
you encounter problems, consider that the VGRA is a fixed size and
a high-capacity physical volume might exceed the total number of physical
extents allowed. As a result, you might need to use a larger-than-default
extent size on high-capacity LVM disks. Conversely, if all LVM disks
in a volume group are small, the default number of extents might make
the VGRA too large, wasting disk and memory space. 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.
User Data Area |
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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.
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