LVM初步

http://www.ibm.com/developerworks/cn/linux/l-lvm2/

 

逻辑卷管理（LVM）指系统将物理卷管理抽象到更高的层次，常常会形成更简单的管理模式。通过使用 LVM，所有物理磁盘和分区，无论它们的大小和分布方式如何，都被抽象为单一存储（single storage）源。例如，在图 1 所示的物理到逻辑映射布局中，最大的磁盘是 80GB 的，那么用户如何创建更大（比如 150GB）的文件系统呢？

图 1. 物理到逻辑的映射 

LVM 可以将分区和磁盘聚合成一个虚拟磁盘（virtual disk），从而用小的存储空间组成一个统一的大空间。这个虚拟磁盘在 LVM 术语中称为卷组（volume group）。

建立比最大的磁盘还大的文件系统并不是这种高级存储管理方法的惟一用途。还可以使用 LVM 完成以下任务：

• 在磁盘池中添加磁盘和分区，对现有的文件系统进行在线扩展
• 用一个 160GB 磁盘替换两个 80GB 磁盘，而不需要让系统离线，也不需要在磁盘之间手工转移数据
• 当存储空间超过所需的空间量时，从池中去除磁盘，从而缩小文件系统
• 使用快照（snapshot）执行一致的备份（本文后面会进一步讨论）

LVM2 是一个新的用户空间工具集，它为 Linux 提供逻辑卷管理功能。它完全向后兼容原来的 LVM 工具集。在本文中，将介绍 LVM2 最有用的特性以及几种简化系统管理任务的方法。（随便说一句，如果您正在寻找关于 LVM 的基本指南，那么可以看看参考资料 中列出的 LVM HowTo。）

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Name

lvm - LVM2 tools

Synopsis

lvm [command | file]

Description

lvm provides the command-line tools for LVM2. A separate manual page describes each command in detail.

If lvm is invoked with no arguments it presents a readline prompt (assuming it was compiled with readline support). LVM commands may be entered interactively at this prompt with readline facilities including history and command name and option completion. Refer to readline(3) for details.

If lvm is invoked with argv[0] set to the name of a specific LVM command (for example by using a hard or soft link) it acts as that command.

On invocation, lvm requires that only the standard file descriptors stdin, stdout and stderr are available. If others are found, they get closed and messages are issued warning about the leak.

Where commands take VG or LV names as arguments, the full path name is optional. An LV called "lvol0" in a VG called "vg0" can be specified as "vg0/lvol0". Where a list of VGs is required but is left empty, a list of all VGs will be substituted. Where a list of LVs is required but a VG is given, a list of all the LVs in that VG will be substituted. So "lvdisplay vg0" will display all the LVs in "vg0". Tags can also be used - seeaddtag below.

One advantage of using the built-in shell is that configuration information gets cached internally between commands.

A file containing a simple script with one command per line can also be given on the command line. The script can also be executed directly if the first line is #! followed by the absolute path oflvm.

Built-in Commands

The following commands are built into lvm without links normally being created in the filesystem for them.

dumpconfig -- Display the configuration information after

loading lvm.conf (5) and any other configuration files.

formats -- Display recognised metadata formats.

help -- Display the help text.

pvdata -- Not implemented in LVM2.

segtypes -- Display recognised logical volume segment types.

version -- Display version information.

Commands

The following commands implement the core LVM functionality.

pvchange -- Change attributes of a physical volume.

pvck -- Check physical volume metadata.

pvcreate -- Initialize a disk or partition for use by LVM.

pvdisplay -- Display attributes of a physical volume.

pvmove -- Move physical extents.

pvremove -- Remove a physical volume.

pvresize -- Resize a disk or partition in use by LVM2.

pvs -- Report information about physical volumes.

pvscan -- Scan all disks for physical volumes.

vgcfgbackup -- Backup volume group descriptor area.

vgcfgrestore -- Restore volume group descriptor area.

vgchange -- Change attributes of a volume group.

vgck -- Check volume group metadata.

vgconvert -- Convert volume group metadata format.

vgcreate -- Create a volume group.

vgdisplay -- Display attributes of volume groups.

vgexport -- Make volume groups unknown to the system.

vgextend -- Add physical volumes to a volume group.

vgimport -- Make exported volume groups known to the system.

vgimportclone -- Import and rename duplicated volume group (e.g. a hardware snapshot).

vgmerge -- Merge two volume groups.

vgmknodes -- Recreate volume group directory and logical volume special files

vgreduce -- Reduce a volume group by removing one or more physical volumes.

vgremove -- Remove a volume group.

vgrename -- Rename a volume group.

vgs -- Report information about volume groups.

vgscan -- Scan all disks for volume groups and rebuild caches.

vgsplit -- Split a volume group into two, moving any logical volumes from one volume group to another by moving entire physical volumes.

lvchange -- Change attributes of a logical volume.

lvconvert -- Convert a logical volume from linear to mirror or snapshot.

lvcreate -- Create a logical volume in an existing volume group.

lvdisplay -- Display attributes of a logical volume.

lvextend -- Extend the size of a logical volume.

lvmchange -- Change attributes of the logical volume manager.

lvmdiskscan -- Scan for all devices visible to LVM2.

lvmdump -- Create lvm2 information dumps for diagnostic purposes.

lvreduce -- Reduce the size of a logical volume.

lvremove -- Remove a logical volume.

lvrename -- Rename a logical volume.

lvresize -- Resize a logical volume.

lvs -- Report information about logical volumes.

lvscan -- Scan (all disks) for logical volumes.

The following commands are not implemented in LVM2 but might be in the future: lvmsadc, lvmsar, pvdata.

Options

The following options are available for many of the commands. They are implemented generically and documented here rather than repeated on individual manual pages.

-h | --help -- Display the help text.

--version -- Display version information.

-v | --verbose -- Set verbose level.

Repeat from 1 to 3 times to increase the detail of messages sent to stdout and stderr. Overrides config file setting.

-d | --debug -- Set debug level.

Repeat from 1 to 6 times to increase the detail of messages sent to the log file and/or syslog (if configured). Overrides config file setting.

--quiet -- Suppress output and log messages.

Overrides -d and -v.

-t | --test -- Run in test mode.

Commands will not update metadata. This is implemented by disabling all metadata writing but nevertheless returning success to the calling function. This may lead to unusual error messages in multi-stage operations if a tool relies on reading back metadata it believes has changed but hasn't.

--driverloaded { y | n }

Whether or not the device-mapper kernel driver is loaded. If you set this to n, no attempt will be made to contact the driver.

-A | --autobackup { y | n }

Whether or not to metadata should be backed up automatically after a change. You are strongly advised not to disable this! Seevgcfgbackup (8).

-P | --partial

When set, the tools will do their best to provide access to volume groups that are only partially available (one or more physical volumes belonging to the volume group are missing from the system). Where part of a logical volume is missing,/dev/ioerror will be substituted, and you could use dmsetup (8) to set this up to return I/O errors when accessed, or create it as a large block device of nulls. Metadata may not be changed with this option. To insert a replacement physical volume of the same or large size use pvcreate -u to set the uuid to match the original followed byvgcfgrestore (8).

-M | --metadatatype type

Specifies which type of on-disk metadata to use, such as lvm1 orlvm2, which can be abbreviated to1 or 2 respectively. The default (lvm2) can be changed by settingformat in theglobal section of the config file.

--ignorelockingfailure

This lets you proceed with read-only metadata operations such as lvchange -ay andvgchange -ay even if the locking module fails. One use for this is in a system init script if the lock directory is mounted read-only when the script runs.

--addtag tag

Add the tag tag to a PV, VG or LV. Supply this argument multiple times to add more than one tag at once. A tag is a word that can be used to group LVM2 objects of the same type together. Tags can be given on the command line in place of PV, VG or LV arguments. Tags should be prefixed with @ to avoid ambiguity. Each tag is expanded by replacing it with all objects possessing that tag which are of the type expected by its position on the command line. PVs can only possess tags while they are part of a Volume Group: PV tags are discarded if the PV is removed from the VG. As an example, you could tag some LVs asdatabase and others asuserdata and then activate the database ones withlvchange -ay @database. Objects can possess multiple tags simultaneously. Only the new LVM2 metadata format supports tagging: objects using the LVM1 metadata format cannot be tagged because the on-disk format does not support it. Snapshots cannot be tagged. Characters allowed in tags are: A-Z a-z 0-9 _ + . - and as of version 2.02.78 the following characters are also accepted: / = ! : # &

--deltag tag

Delete the tag tag from a PV, VG or LV, if it's present. Supply this argument multiple times to remove more than one tag at once.

--alloc AllocationPolicy

The allocation policy to use: contiguous, cling,normal,anywhere or inherit. When a command needs to allocate physical extents from the volume group, the allocation policy controls how they are chosen. Each volume group and logical volume has an allocation policy. The default for a volume group is normal which applies common-sense rules such as not placing parallel stripes on the same physical volume. The default for a logical volume isinherit which applies the same policy as for the volume group. These policies can be changed usinglvchange (8) and vgchange (8) or over-ridden on the command line of any command that performs allocation. Thecontiguous policy requires that new extents be placed adjacent to existing extents. Thecling policy places new extents on the same physical volume as existing extents in the same stripe of the Logical Volume. If there are sufficient free extents to satisfy an allocation request butnormal doesn't use them,anywhere will - even if that reduces performance by placing two stripes on the same physical volume.

N.B. The policies described above are not implemented fully yet.

In particular, contiguous free space cannot be broken up to satisfy allocation attempts.

Environment Variables

LVM_SYSTEM_DIR

Directory containing lvm.conf and other LVM system files. Defaults to "/etc/lvm".

HOME

Directory containing .lvm_history if the internal readline shell is invoked.

LVM_VG_NAME

The volume group name that is assumed for any reference to a logical volume that doesn't specify a path. Not set by default.

Valid Names

The following characters are valid for VG and LV names: a-z A-Z 0-9 + _ . -

VG and LV names cannot begin with a hyphen. There are also various reserved names that are used internally by lvm that can not be used as LV or VG names. A VG cannot be called anything that exists in /dev/ at the time of creation, nor can it be called '.' or '..'. A LV cannot be called '.' '..' 'snapshot' or 'pvmove'. The LV name may also not contain the strings '_mlog' or '_mimage'

Diagnostics

All tools return a status code of zero on success or non-zero on failure.

Files

/etc/lvm/lvm.conf
$HOME/.lvm_history

See Also

clvmd(8), lvchange(8),lvcreate(8),lvdisplay(8),lvextend(8),lvmchange(8),lvmdiskscan(8),lvreduce(8),lvremove(8),lvrename(8),lvresize(8),lvs(8),lvscan(8),pvchange(8),pvck(8),pvcreate(8),pvdisplay(8),pvmove(8),pvremove(8),pvs(8),pvscan(8),vgcfgbackup(8),vgchange(8),vgck(8),vgconvert(8),vgcreate(8),vgdisplay(8),vgextend(8),vgimport(8),vgimportclone(8),vgmerge(8),vgmknodes(8),vgreduce(8),vgremove(8),vgrename(8),vgs(8),vgscan(8),vgsplit(8),readline(3),lvm.conf(5)

Referenced By

cmirrord(8), dmeventd(8),fsadm(8),gfs2_mount(8),gfs_mount(8),guestfs(3),lvconvert(8),lvmconf(8),lvmsadc(8),lvmsar(8),mount.gfs2(8),pvresize(8),resize2fs(8),vgcfgrestore(8),vgexport(8),virt-resize(1),xfs_freeze(8),xfs_info(8)