Installation guide

Chapter 1. The LVM Logical Volume Manager
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• 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:
Figure 1.1. LVM Logical Volume Components
For detailed information on the components of an LVM logical volume, see Chapter 2, LVM
Components.
1.4. The Clustered Logical Volume Manager (CLVM)
The Clustered Logical Volume Manager (CLVM) is a set of clustering extensions to LVM. These
extensions allow a cluster of computers to manage shared storage (for example, on a SAN) using
LVM. CLVM is part of the Resilient Storage Add-On.
Whether you should use CLVM depends on your system requirements:
• If only one node of your system requires access to the storage you are configuring as logical
volumes, then you can use LVM without the CLVM extensions and the logical volumes created with
that node are all local to the node.