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HP-UX System Administrator's Guide: Logical Volume Management: HP-UX 11i Version 3 > Chapter 1 Introduction

LVM Disk Layout


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NOTE: This information applies only to disks belonging to Version 1.0 volume groups.

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

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

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

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

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

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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