Red Hat Enterprise Linux 6 LVM管理员手册（6.4版）

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本资源是《Red Hat Enterprise Linux 6逻辑卷管理员手册》（Red Hat Enterprise Linux 6 Logical Volume Manager Administration），它是一份详细的指南，专为RHEL 6的逻辑卷管理（LVM）管理员设计，已更新至6.4版本。这份文档由Red Hat Inc.发布，遵循Creative Commons Attribution-ShareAlike 3.0 Unported (CC-BY-SA) 许可协议，这意味着用户在分享、复制或修改这份文档时，必须提供原始版本的链接并保持同样开放许可。版权方面，2012年及以后，Red Hat拥有该手册的文本和插图，但在法律允许的范围内，根据CC-BY-SA，他们放弃了一些权利，并同意不强制执行第4d条。在使用过程中，用户应确保遵守这些条款。手册涵盖了Red Hat Enterprise Linux 6（RHEL 6）环境中LVM管理员所需的关键知识点，包括但不限于： 1. **概述**：LVM（Logical Volume Manager）是用于管理和扩展存储的一种动态分配和分区技术，使得系统可以更高效地利用磁盘空间，实现数据卷的创建、扩展、迁移和备份。 2. **安装与配置**：介绍如何在RHEL 6系统中安装和配置LVM，包括安装LVM工具、创建逻辑卷组（VG）、添加物理卷（PV）以及创建和挂载逻辑卷。 3. **卷组管理**：讲解如何管理卷组，如创建、删除、扩展卷组，以及监控卷组状态。 4. **逻辑卷操作**：详细介绍如何创建、调整大小、复制和删除逻辑卷，以及在不同系统间迁移逻辑卷。 5. **配额和性能**：探讨如何使用LVM来设置文件系统的配额，以及优化I/O性能和提高数据安全性。 6. **高级特性**：涉及诸如镜像卷（Mirrored Volumes）、RAID-1、RAID-5和RAID-6等高级LVM功能的创建和使用。 7. **故障恢复与备份**：提供了关于如何处理LVM故障、数据恢复以及定期备份逻辑卷的重要步骤。 8. **安全和权限**：讨论了LVM权限管理，确保正确地授予和限制对逻辑卷的操作。 9. **许可证和法律注意事项**：再次强调了CC-BY-SA许可协议的适用性和Red Hat的商标政策，包括Linux、Java、XFS等其他注册商标的使用规范。作为RHEL 6系统管理员的必备参考资料，这份手册提供了丰富的实践指导，有助于用户充分利用LVM的优势，提升系统存储管理的灵活性和效率。

To ensure that clvmd is started at boot time, you can execute a chkconfig ... on command on the

clvmd service, as follows:

# chkco nfig clvmd on

If the clvmd daemon has not been started, you can execute a service ... start command on the

clvmd service, as follows:

# servi ce clvmd start

Creating LVM logical volumes in a cluster environment is identical to creating LVM logical volumes on a

single node. T here is no difference in the LVM commands themselves, or in the LVM graphical user

interface, as described in Chapter 4, LVM Administration with CLI Commands and Chapter 7, LVM

Administration with the LVM GUI. In order to enable the LVM volumes you are creating in a cluster, the

cluster infrastructure must be running and the cluster must be quorate.

By default, logical volumes created with CLVM on shared storage are visible to all systems that have

access to the shared storage. It is possible to create volume groups in which all of the storage devices

are visible to only one node in the cluster. It is also possible to change the status of a volume group from

a local volume group to a clustered volume group. For information, see Section 4.3.2, “Creating Volume

Groups in a Cluster” and Section 4.3.7, “Changing the Parameters of a Volume Group”.

Warning

When you create volume groups with CLVM on shared storage, you must ensure that all nodes in

the cluster have access to the physical volumes that constitute the volume group. Asymmetric

cluster configurations in which some nodes have access to the storage and others do not are not

supported.

Figure 1.2, “CLVM Overview” shows a CLVM overview in a cluster.

16 Chapter 1. The LVM Logical Volume Manager

Chapter 2. LVM Components

This chapter describes the components of an LVM Logical volume.

2.1. Physical Volumes

The underlying physical storage unit of an LVM logical volume is a block device such as a partition or

whole disk. To use the device for an LVM logical volume the device must be initialized as a physical

volume (PV). Initializing a block device as a physical volume places a label near the start of the device.

By default, the LVM label is placed in the second 512-byte sector. You can overwrite this default by

placing the label on any of the first 4 sectors. This allows LVM volumes to co-exist with other users of

these sectors, if necessary.

An LVM label provides correct identification and device ordering for a physical device, since devices can

come up in any order when the system is booted. An LVM label remains persistent across reboots and

throughout a cluster.

The LVM label identifies the device as an LVM physical volume. It contains a random unique identifier

(the UUID) for the physical volume. It also stores the size of the block device in bytes, and it records

where the LVM metadata will be stored on the device.

The LVM metadata contains the configuration details of the LVM volume groups on your system. By

default, an identical copy of the metadata is maintained in every metadata area in every physical volume

within the volume group. LVM metadata is small and stored as ASCII.

Currently LVM allows you to store 0, 1 or 2 identical copies of its metadata on each physical volume. T he

default is 1 copy. Once you configure the number of metadata copies on the physical volume, you cannot

change that number at a later time. T he first copy is stored at the start of the device, shortly after the

label. If there is a second copy, it is placed at the end of the device. If you accidentally overwrite the area

at the beginning of your disk by writing to a different disk than you intend, a second copy of the metadata

at the end of the device will allow you to recover the metadata.

For detailed information about the LVM metadata and changing the metadata parameters, see

Appendix D, LVM Volume Group Metadata.

2.1.1. LVM Physical Volume Layout

Figure 2.1, “Physical Volume layout” shows the layout of an LVM physical volume. T he LVM label is on

the second sector, followed by the metadata area, followed by the usable space on the device.

Note

In the Linux kernel (and throughout this document), sectors are considered to be 512 bytes in

size.

Red Hat Enterprise Linux 6 Logical Volume Manager Administration 19

Figure 2.1. Physical Volume layout

2.1.2. 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. T his

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 cannot 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. T his would result in a decrease in performance rather than an

increase.

Although 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 striped volumes.

2.2. Volume Groups

Physical volumes are combined into volume groups (VGs). T his creates a pool of disk space out of

which logical volumes can be allocated.

Within a volume group, the disk space available for allocation is divided into units of a fixed-size called

extents. An extent is the smallest unit of space that can be allocated. Within a physical volume, extents

are referred to as physical extents.

A logical volume is allocated into logical extents of the same size as the physical extents. The extent

size is thus the same for all logical volumes in the volume group. The volume group maps the logical

extents to physical extents.

2.3. LVM Logical Volumes

20 Chapter 2. LVM Components

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