Novell LINUX ENTERPRISE SERVER 10 - INSTALLATION AND ADMINISTRATION 11-05-2007, Installation Manual

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7.1.1 The Logical Volume Manager
The Logical Volume Manager (LVM) enables flexible distribution of hard disk space
over several file systems. It was developed because sometimes the need to change the
segmentation of hard disk space arises only after the initial partitioning during installation
has already been done. Because it is difficult to modify partitions on a running system,
LVM provides a virtual pool (volume group, VG for short) of memory space from
which logical volumes (LVs) can be created as needed. The operating system accesses
these LVs instead of the physical partitions. Volume groups can span more than only
one disk so that several disks or parts of them may constitute one single VG. This way,
LVM provides a kind of abstraction from the physical disk space that allows its segmen-
tation to be changed in a much easier and safer way than physical repartitioning does.
Background information regarding physical partitioning can be found in
Section “Par-
tition Types” (page 151) and Section 8.5.7, “Using the YaST Partitioner” (page 149).
Figure 7.1 Physical Partitioning versus LVM
PART PART PART PART PART
DISK
PART PART PART
MP MP MP MP MP MP MP
DISK 1 DISK 2
VG 1 VG 2
LV 1 LV 2 LV 3 LV 4
Figure 7.1, “Physical Partitioning versus LVM” (page 112) compares physical partitioning
(left) with LVM segmentation (right). On the left side, one single disk has been divided
into three physical partitions (PART), each with a mount point (MP) assigned so that
the operating system can access them. 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 defined. 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 logical volumes (LV 1 through LV 4) have been defined,
which can be used by the operating system via the associated mount points. The border
112 Installation and Administration