2.2 LVM Configuration
This section briefly describes the principles behind the Logical Volume
Manager (LVM) and its basic features that make it useful under many
circumstances. In Section 2.2.2, LVM Configuration with YaST, learn how
to set up LVM with YaST.
Using LVM might be associated with increased risk, such as data loss.
Risks also include application crashes, power failures, and faulty
commands. Save your data before implementing LVM or reconfiguring
volumes. Never work without a backup.
2.2.1 The Logical Volume Manager
The 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 segmentation to be changed
in a much easier and safer way than physical repartitioning does.
Background information regarding physical partitioning can be found in
Section 2.1.1, Partition Types and
Section 2.1, Using the YaST Partitioner.
Figure 2-2 Physical Partitioning versus LVM
Figure 2-2 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 LVs (LV 1 through LV 4) have been defined, which
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.
Several hard disks or partitions can be combined in a large logical
Provided the configuration is suitable, an LV (such as
/usr) can be enlarged when the free space is
Using LVM, it is possible to add hard disks or LVs in a running system.
However, this requires hot-swappable hardware that is capable of such
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, this can improve the reading and writing performance just like
The snapshot feature enables consistent backups (especially for
servers) in the running system.
With these features, using LVM already makes sense for heavily used home
PCs or small servers. If you have a growing data stock, as in the case of
databases, music archives, or user directories, LVM is just the right
thing for you. This would allow file systems that are larger than the
physical hard disk. Another advantage of LVM is that up to 256 LVs can be
added. However, keep in mind that working with LVM is different from
working with conventional partitions. Instructions and further
information about configuring LVM is available in the official LVM HOWTO
Starting from kernel version 2.6, LVM version 2 is available,
which is downward-compatible 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 downward-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
version 2. Therefore, when talking about LVM, this section always
refers to LVM version 2.
2.2.2 LVM Configuration with YaST
The YaST LVM configuration can be reached from the YaST Expert
Partitioner (see Section 2.1, Using the YaST Partitioner). This
partitioning tool enables you to edit and delete existing partitions and
create new ones that should be used with LVM. The first task is to create
PVs that provide space to a volume group: There, create an LVM partition
by first selecting a hard disk, then clicking
, and finally selecting as the partition identifier. After creating all the
partitions to use with LVM, click to
start the LVM configuration.
Select a hard disk from .
Change to the tab.
Click and enter the desired size of the PV on
Use and change the
Do not mount this partition.
Repeat this procedure until you defined all the desired physical
volumes on the available disks.
Creating Volume Groups
If no volume group exists on your system yet, you are prompted to add
one (see Figure 2-3). It is possible to create
additional groups with , but usually
one single volume group is sufficient. system is
suggested as a name for the volume group in which the openSUSE®
system files are located. The physical extent size defines the size of a
physical block in the volume group. All the disk space in a volume group
is handled in chunks of this size. This value is normally set to
4 MB and allows for a maximum size of 256 GB for physical and LVs.
The physical extent size should only be increased, for example, to 8,
16, or 32 MB, if you need LVs larger than 256 GB.
Figure 2-3 Creating a Volume Group
Add the previously defined PVs to the volume group by selecting them
with the mouse and using
. Check if the
resulting size at the bottom line of has the right value.
If you have multiple volume groups defined, and want to add or remove
PVs, select the volume group in
Then change to the tab and select
. In the following menu, you can add or remove
PVs to the selected volume group.
Configuring Logical Volumes
After the volume group has been filled with PVs, define the LVs the
operating system should use in the next dialog. Set the current volume
group in a selection box to the upper left. Next to it, the free space
in the current volume group is shown. The list below contains all LVs in
that volume group. All normal Linux partitions to which a mount point is
assigned, all swap partitions, and all already existing LVs are listed
, , and
LVs as needed until all space in the volume
group has been exhausted. Assign at least one LV to each volume group.
Figure 2-4 Logical Volume Management
To create a new LV, select the volume group in
and change to the tab. There, click and go
through the wizard-like popup that opens:
Enter the name of the LV. For a partition that should be mounted to
/home, a selfexplaining name like
HOME could be used.
Select the size and the number of stripes of the LV. If you have only
one PV, selecting more than one stripes is not useful.
Choose the filesystem to use on the LV as well as the mount point.
By using stripes it is possible to distribute the data stream in the LV
among several PVs (striping). If these PVs reside on different hard
disks, this generally results in a better reading and writing
performance (like RAID 0). However, a striping LV with
n stripes can only be created correctly if the hard
disk space required by the LV can be distributed evenly to
n PVs. If, for example, only two PVs are available, a
LV with three stripes is impossible.
YaST has no chance at this point to verify the correctness of your
entries concerning striping. Any mistake made here is apparent only
later when the LVM is implemented on disk.
If you have already configured LVM on your system, the existing logical
volumes can also be used. Before continuing, assign appropriate mount
points to these LVs, too. With
, return to the
YaST Expert Partitioner and finish your work there.