Red Hat LVM ADMINISTRATOR 5.0 Manuel d'utilisateur télécharger pdf (Page 3)

Implementing LVM during a Linux installation

Because storage management is one of the main challenges

system administrators regularly face, most major Linux distri-

butions have included LVM with their installers, simplifying the

task of LVM deployment. For instance, Red Hat Linux included

LVM starting with its 8.0 release. Although LVM can be intro-

duced during system installation or any time after, this article

discusses only the case of deploying LVM during Red Hat Linux

installation and modifying storage volumes afterward. Migration

of an already installed system to LVM can be complex, especially

if it involves moving any file systems required for system

boot, such as root and boot, to an LVM volume.

An important problem administrators must address when

installing Linux is how best to partition and allocate system stor-

age. Predicting how these partitions will be used during the life-

time of the system can be difficult. Even though storage on Linux

systems can be expanded by adding more disks or storage enclo-

sures, expanding or modifying existing partitions is very risky,

if not impossible. LVM greatly simplifies the task of expanding

or modifying partitions.

For data protection and integrity, Dell strongly suggests using

a Dell PowerEdge Expandable RAID Controller (PERC) or Dell Cost-

Effective RAID Controller (CERC) implementing a RAID level of 1,

5, or higher, depending on system needs.

Planning storage partitions and allocations

Before installing Linux, administrators should plan how to partition

and allocate their storage. They should also evaluate how much risk

and complexity they are willing to handle in order to recover a

failed system. For example, creating root and boot partitions out-

side LVM makes system recovery easier by eliminating the need to

activate LVM when rescuing a failed system. Also, those using Linux

Loader (LILO) as the preferred boot loader should be aware that it

does not support LVM. Administrators using LILO must put the

boot partition outside LVM.

Although LVM can be used with several file system types, such

as ext2, ext3, and ReiserFS, this article addresses only ext3, the

default Red Hat Linux file system. Figure 3 shows an example par-

titioning scheme; the installation steps described in the following

sections use these values.

Using Disk Druid for manual partitioning

Implementing a partitioning scheme such as the one shown in

Figure 3 during installation of Red Hat Linux 9 Professional is

straightforward. The LVM feature is available only in the graphical

user interface (GUI) installation mode. To use this feature, boot the

system by using the Red Hat Linux 9 CD 1. At the boot prompt,

press the Enter key to install in GUI mode. At the Disk Partitioning

Setup screen, select “Manually partition with Disk Druid,” followed

by “Next.”

When the Disk Druid menu is displayed, administrators can use

the New button to create both boot and root partitions on the first

hard drive, /dev/sda. Then, selecting the remaining free space of

/dev/sda to edit and setting the file system to LVM enables admin-

istrators to create physical volumes on the remaining space of the

first drive. This step can be repeated for all the remaining hard

drives. Selecting the LVM button on the Disk Druid screen launches

the Make LVM Volume Group window.

From this window, administrators can add, edit, and delete

logical volume groups. Other possible actions include setting the

volume group name and physical

extent size (the default is 4 MB)

and choosing the hard drive on

which to create the logical volume.

The Add and Edit buttons allow

administrators to set the mount

point, size, file system type, and

name of the planned logical vol-

umes (see Figure 4).

If implemented using the

default setting of 4 MB per phys-

ical extent, a volume group is

limited to 255 GB because only

65,534 physical or logical extents

are allowed in a volume group.

To provide more than 256 GB

in a volume group, administra-

tors must create the physical

extents in chunk sizes larger

than 4 MB. Physical extents

must be a power of 2 and can

range anywhere between 8 KB

STORAGE ENVIRONMENT

www.dell.com/powersolutions POWER SOLUTIONS

113

File system File system Logical

mount point Size (MB) type LVM group* volume name

/ 6144 ext3 None None

/boot 128 ext3 None None

Logical volume File system Logical

mount point Size (MB) type LVM group volume name

/home 4096 ext3 lvm00 lvm_home

/usr 6144 ext3 lvm00 lvm_usr

/var 6144 ext3 lvm00 lvm_var

/data 4096 ext3 lvm00 lvm_data

*Neither the root nor boot partitions use LVM.

Figure 3. Example partition values

Even though storage on

Linux systems can be

expanded by adding

more disks or storage

enclosures, expanding

or modifying existing

partitions is very risky,

if not impossible. LVM

greatly simplifies the

task of expanding or

modifying partitions.

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