AIX Version 4.3 Differences Guide

The LVM in AIX 4.3.2 supports both the small VG configurations of the previous
versions of AIX and the new big VG configuration. A migration path is provided to
convert old volume groups to the new volume group format, provided there are
sufficient free partitions on each of the physical volumes in the volume group to
be allocated.
The following sections explain the changes for the bigger VGDA/VGSA, which
describe a volume group to a system completely. The changes needed for
commands, library, and the LV device driver are also discussed.
5.6.1 Changes to LVCB
The original design of the VGDA and VGSA limited the number of disks that can
be added to the volume group at 32 and the total number of logical volumes at
256 (including one reserved for LVM internal use). With the increasing use of disk
arrays, the need for the increased capacity for a single volume group is greater.
Following are the basic concepts of VGDA, VGSA, and LVCB.
VGDA Stands for volume group descriptor area. The VGDA contains
information that describes the mapping of physical partitions to logical
partitions for each logical volume in the volume group, as well as other
vital information, including a time stamp. The VGDA is stored on each
physical volume of the volume group.
VGSA Stands for volume group status area. VGSA contains information,
such as which physical partitions are stale and which physical
volumes are missing (that is, not available or active), when a vary-on
operation is attempted on a volume group. The VGSA is stored on
each physical volume of the volume group.
LVCB Stands for logical volume control block. The LVCB is the first 512 bytes
of a logical volume. This area holds important information, such as the
creation date of the logical volume, information about mirrored copies,
and possible mount points in the journaled filesystem (JFS). Certain
LVM commands are required to update the LVCB as part of the
algorithms in LVM.
The Logical Volume Control Block has been moved from the first block of the
logical volume to inside the VGDA for better preservation. Though database
programs that use logical volumes as raw devices skip this block, obliteration of
the LVCB has caused confusion and loss of information such as intra-policy,
inter-policy, upperbound, and so on. Since other subsystems, such as
diagnostics, IPL, and ROS, do use the LVCB without using the LVM access
routines, the LVCB will be maintained at both places.
5.6.2 General Enhancements for Big VG
The following sections describe the general limitations and updates required to
implement big VG support on AIX.
5.6.2.1 Commands Changes
To support the big VG format, some new options have been added to the
commands mkvg, chvg, importvg, mklv, and chlv commands.
The mkvg Command
The following lists some of the major changes to the mkvg command.
88 AIX Version 4.3 Differences Guide