VERITAS Volume Manager 3.1 Migration Guide

VxVM and LVM
VxVM and LVM—Conceptual Comparison
Chapter 120
User data is contained in physical extents in LVM and subdisks in VxVM.
The LVM physical extents are of a fixed length. LVM allocates space in terms of
physical extents which is a set of physical disk blocks on a physical volume. The
extent size for all physical volumes within a volume group must be the same, and is
usually 4 MB.
VxVM allocates disk space in term of subdisks which is a set of physical disk blocks
representing a specific portion of a VxVM disk and is of arbitrary size.
LVM metadata Private Region
LVM metadata and the Private Region are similar conceptually.
In LVM, metadata is stored in a reserved area in the disk.
In VxVM, the private region of a disk contains various on-disk structures that are
used by the Volume Manager for various internal purposes. Private regions can
also contain copies of a disk group’s configuration, and copies of the disk group’s
kernel log.
Unused Physical Extent Free Space
LVM contains unused physical extents that are not part of a logical volume, but are
part of the volume group.
Similarly, free space is an area of a disk under VxVM that is not allocated to any
subdisk or reserved for use by any other Volume Manager object.
Mirrors Mirrors (Plexes)
Both LVM and VxVM support mirrors. Mirrors can be used to store multiple copies
of a volume’s data on separate disks.
In LVM, you can create mirrors using the MirrorDisk/UX product. Mirrors allow
duplicate copies of the extents to be kept on separate physical volumes.
MirrorDisk/UX supports up to 3 copies of the data.
A VxVM mirror consists of plexes. Each plex is a copy of the volume. A plex consists
of one or more subdisks located on one or more disks. VxVM volumes can have up to
32 mirrors (where each plex is a copy of data). Mirroring features are available with
an additional license.
Export Deport
Table 1-1A Conceptual comparison of LVM and VxVM
LVM Term VxVM Term