Red Hat ENTERPRISE LINUX 5 - LOGICAL VOLUME MANAGER ADMINISTRATION Guide d'installation télécharger pdf (Page 16)

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Figure 2.1. Physical Volume layout

1.2. Multiple Partitions on a Disk

LVM allows you to create physical volumes out of disk partitions. It is generally recommended

that you create a single partition that covers the whole disk to label as an LVM physical volume

for the following reasons:

• Administrative convenience

It is easier to keep track of the hardware in a system if each real disk only appears once.

This becomes particularly true if a disk fails. In addition, multiple physical volumes on a

single disk may cause a kernel warning about unknown partition types at boot-up.

• Striping performance

LVM can not tell that two physical volumes are on the same physical disk. If you create a

striped logical volume when two physical volumes are on the same physical disk, the stripes

could be on different partitions on the same disk. This would result in a decrease in perform-

ance rather than an increase.

Although it it is not recommended, there may be specific circumstances when you will need to

divide a disk into separate LVM physical volumes. For example, on a system with few disks it

may be necessary to move data around partitions when you are migrating an existing system to

LVM volumes. Additionally, if you have a very large disk and want to have more than one

volume group for administrative purposes then it is necessary to partition the disk. If you do

have a disk with more than one partition and both of those partitions are in the same volume

group, take care to specify which partitions are to be included in a logical volume when creating

1.2. Multiple Partitions on a Disk

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Red Hat ENTERPRISE LINUX 5 - LOGICAL VOLUME MANAGER ADMINISTRATION Guide d'installation Page 16