Operation Manual
the operating system can gain access. On the right side, two disks have been divided
into two and three physical partitions each. Two LVM volume groups (VG 1 and VG 2)
have been dened. VG 1 contains two partitions from DISK 1 and one from DISK 2.
VG 2 contains the remaining two partitions from DISK 2. In LVM, the physical disk
partitions that are incorporated in a volume group are called physical volumes (PVs).
Within the volume groups, four LVs (LV 1 through LV 4) have been dened. They
can be used by the operating system via the associated mount points. The border between
different LVs need not be aligned with any partition border. See the border between
LV 1 and LV 2 in this example.
LVM features:
• Several hard disks or partitions can be combined in a large logical volume.
•
Provided the conguration is suitable, an LV (such as /usr) can be enlarged if
free space is exhausted.
• With LVM, it is possible to add hard disks or LVs in a running system. However,
this requires hot-swappable hardware.
• It is possible to activate a "striping mode" that distributes the data stream of a LV
over several PVs. If these PVs reside on different disks, the read and write perfor-
mance is enhanced, as with RAID 0.
• The snapshot feature enables consistent backups (especially for servers) in the
running system.
With these features, LVM is ready for heavily used home PCs or small servers. LVM
is well-suited for the user with a growing data stock (as in the case of databases, music
archives, or user directories). This would allow le systems that are larger than the
physical hard disk. Another advantage of LVM is that up to 256 LVs can be added.
However, working with LVM is different from working with conventional partitions.
Instructions and further information about conguring LVM is available in the ofcial
LVM HOWTO at http://tldp.org/HOWTO/LVM-HOWTO/.
Starting from kernel version 2.6, LVM version 2 is available, which is backward-com-
patible with the previous LVM and enables the continued management of old volume
groups. When creating new volume groups, decide whether to use the new format or
the backward-compatible version. LVM 2 does not require any kernel patches. It makes
use of the device mapper integrated in kernel 2.6. This kernel only supports LVM ver-
sion 2. Therefore, when talking about LVM, this section always refers to LVM version 2.
Advanced Disk Setup 49