Red Hat GLOBAL FILE SYSTEM 5.0, Administrator'S Manual

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Using logical volumes, you can take device snapshots for consistent backups or to test the
effect of changes without affecting the real data.
The implementation of these features in LVM is described in the remainder of this document.
2. LVM Architecture Overview
For the RHEL 4 release of the Linux operating system, the original LVM1 logical volume
manager was replaced by LVM2, which has a more generic kernel framework than LVM1. LVM2
provides the following improvements over LVM1:
• flexible capacity
• more efficient metadata storage
• better recovery format
• new ASCII metadata format
• atomic changes to metadata
• redundant copies of metadata
LVM2 is backwards compatible with LVM1, with the exception of snapshot and cluster support.
You can convert a volume group from LVM1 format to LVM2 format with the
vgconvert
command. For information on converting LVM metadata format, see the
vgconvert
(8) man
page.
The underlying physical storage unit of an LVM logical volume is a block device such as a
partition or whole disk. This device is initialized as an LVM physical volume (PV).
To create an LVM logical volume, the physical volumes are combined into a volume group (VG).
This creates a pool of disk space out of which LVM logical volumes (LVs) can be allocated. This
process is analogous to the way in which disks are divided into partitions. A logical volume is
used by file systems and applications (such as databases).
Figure 1.1, “LVM Logical Volume Components” shows the components of a simple LVM logical
volume:
Chapter 1. The LVM Logical Volume Manager
2