Veritas Volume Manager 5.0 Migration Guide, HP-UX 11i v3, First Edition, May 2008

10 VxVM and LVM
VxVM and LVM—conceptual comparison
VxVM and LVM—conceptual comparison
The following section compares the terminology used in LVM and VxVM at a
conceptual level. For more information, refer to the glossary of this Guide for
precise and detailed definitions of these terms.
Table 1-1 A conceptual comparison of LVM and VxVM
LVM term VxVM term
LVM Vx VM
Both LVM and VxVM enable online disk storage management. They both build virtual
devices, called volumes, on physical disks. Volumes are not limited by the underlying
physical disks, and can include other virtual objects such as mirrors. Volumes are
accessed through the HP-UX file system, a database, or other applications in the same
manner as physical disks would be accessed.
Physical volume VxVM disk
An LVM physical volume and a VxVM disk are conceptually the same. A physical disk is
the basic storage device (media) where the data is ultimately stored. You can access the
data on a physical disk by using a device name (devname) to locate the disk.
In LVM, a disk that has been initialized by LVM becomes known as a physical volume.
A VxVM disk is one that is placed under the Volume Manager control and is added to a
disk group.
VxVM can place a disk under its control without adding it to a disk group. The VxVM
Storage Administrator shows these disks as “free space pool”.
Logical volume Volume
An LVM logical volume and a VxVM volume are conceptually the same. Both are virtual
disk devices that appear to applications, databases, and file systems like physical disk
devices, but do not have the physical limitations of physical disk devices. Due to its
virtual nature, a volume (LVM or VxVM) is not restricted to a particular disk or a specific
area of a disk.
An LVM volume is composed of fixed length extents. LVM volumes can be mirrored or
striped, but mirrored-stripe and striped-mirror layouts are not supported.
VxVM volumes consist of one or more plexes/mirrors holding a copy of the data in the
volume which in turn are made up of subdisks with arbitrary length. The configuration of
a volume can be changed by using the VxVM user interfaces. See the Veritas Volume
Manager Administrator’s Guide for more information. VxVM volumes can be
concatenated, mirrored, striped, RAID-5 or combinations such as mirrored-stripe,
striped-mirror, and concatenated-mirror.