VERITAS Volume Manager 3.5 Migration Guide (August 2002)

VxVM and LVM—Conceptual Comparison Final 24 July 2002
4 VERITAS Volume Manager Migration Guide
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. A Conceptual comparison of LVM and VxVM
LVM Term VxVM Term
LVM VxVM
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 physicalvolume anda VxVMdisk areconceptually thesame. Aphysical diskis thebasic
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.
VxVM volumes consist of one or more plexes/mirrors holding a copy of the data in the volume
which inturn are madeup ofsubdisks witharbitrary length. The configuration ofa volumecan be
changed by using the VxVM user interfaces. See the VERITAS Volume Manager Administrator’s
Guide for more information. VxVM volumes can be one of four types: mirrored, RAID-5, striped,
or concatenated.