lvm: lvm的使用
目录
说明
LVM是”Logical Volume Management”的简称，lvm-howto中做了详细介绍。
可以通过命令lvm进行管理。
$lvm
lvm> vgs
VG #PV #LV #SN Attr VSize VFree
VolGroup00 1 2 0 wz--n- 39.50g 320.00m
vg11 2 1 0 wz--n- 1.99g 1.50g
lvm>
概念
volume group (VG):
The Volume Group is the highest level abstraction used within the LVM.
It gathers together a collection of Logical Volumes and Physical Volumes
into one administrative unit.
physical volume (PV):
A physical volume is typically a hard disk, though it may well just be
a device that 'looks' like a hard disk (eg. a software raid device).
logical volume (LV):
The equivalent of a disk partition in a non-LVM system. The LV is visible
as a standard block device; as such the LV can contain a file system (eg. /home).
physical extent (PE):
Each physical volume is divided chunks of data, known as physical extents,
these extents have the same size as the logical extents for the volume group.
logical extent (LE):
Each logical volume is split into chunks of data, known as logical extents.
The extent size is the same for all logical volumes in the volume group.
总之，VG由多个PV组成，每个PV被划分成大小相同的PE。LV在VG中创建，LV包含的同样大小的LE被映射到不同的PE。
+-- Volume Group --------------------------------+
| |
| +----------------------------------------+ |
| PV | PE | PE | PE | PE | PE | PE | PE | PE | |
| +----------------------------------------+ |
| . . . . |
| . . . . |
| +----------------------------------------+ |
| LV | LE | LE | LE | LE | LE | LE | LE | LE | |
| +----------------------------------------+ |
| . . . . |
| . . . . |
| +----------------------------------------+ |
| PV | PE | PE | PE | PE | PE | PE | PE | PE | |
| +----------------------------------------+ |
| |
+------------------------------------------------+
LE到PE之间的映射可以是线性(linear)分布或者条带(striped)分布。
可以对LV做snapshot，并且可以单独操作snapshot，例如在snapshot中写入，不影响origin。
创建PV
可以将整个磁盘做成PV:
$pvcreate /dev/sdb
Physical volume "/dev/sdb" successfully created.
也可以将磁盘分区做成PV:
$pvcreate /dev/sdc1
Physical volume "/dev/sdc1" successfully created.
如果将整个磁盘做成PV，磁盘头块中存储的是LVM的信息，一些操作系统可能不识别。
可以通过创建一个占满整个磁盘的分区，然后将该分区做成PV。
pvs可以查看所有的PV:
$pvs
PV VG Fmt Attr PSize PFree
/dev/sda3 VolGroup00 lvm2 a-- 39.50g 320.00m
/dev/sdb lvm2 --- 1.00g 1.00g
/dev/sdc1 lvm2 --- 1023.00m 1023.00m
创建VG
将已经初始化的PV，添加的VG中:
$vgcreate vg11 /dev/sdb /dev/sdc1
Volume group "vg11" successfully created
vgs可以查看所有的VG:
$vgs
VG #PV #LV #SN Attr VSize VFree
VolGroup00 1 2 0 wz--n- 39.50g 320.00m
vg11 2 0 0 wz--n- 1.99g 1.99g
创建时可以通过-s指定PE的大小，具体情况查看vgcreate -h。
创建VG之后，需要通过重启或下面的命令激活:
$vgchange -a y vg11
0 logical volume(s) in volume group "vg11" now active
删除VG
vgchange -a n my_volume_group
vgremove my_volume_group
在VG中增/删PV
增加:
vgextend my_volume_group /dev/hdc1
删除时，首先通过pvdisplay查看PV是否还在被使用:
$pvdisplay /dev/sdc1
--- Physical volume ---
PV Name /dev/sdc1
VG Name vg11
PV Size 1023.00 MiB / not usable 3.00 MiB
Allocatable yes
PE Size 4.00 MiB
Total PE 255
Free PE 255
Allocated PE 0
PV UUID QAAL6D-KUJl-SDPU-GYKt-DK5l-UpTc-aIWoVt
如果PV还在使用，通过pvmove迁移数据后，删除：
pvmove /dev/hda1
vgreduce my_volume_group /dev/hda1
详情见remove disk。
创建/删除LV
可以通过了解lvcreate的参数，指定更多的条件。
lvcreate -L500 -nlv1 vg11
通过lvs，可以查看所有的lv:
$lvs
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
LogVol00 VolGroup00 -wi-ao---- 37.69g
LogVol01 VolGroup00 -wi-ao---- 1.50g
lv1 vg11 -wi-a----- 500.00m
创建之后，会在/dev/mapper中生成设备文件:
$ls /dev/mapper/
control vg11-lv1 VolGroup00-LogVol00 VolGroup00-LogVol01
可以直接对vg11-lv1格式化，挂载:
mkfs.ext4 /dev/mapper/vg11-lv1
mount /dev/mapper/vg11-lv1 /mnt
将LV卸载之后，可以删除:
umount /dev/mapper/vg11-lv1
lvremove /dev/mapper/vg11-lv1
扩容/缩容LV
扩容:
lvextend -L12G /dev/myvg/homevol
卸载后，缩容:
lvreduce -L-1G /dev/myvg/homevol
对LV进行扩容/缩容操作之后，还需要调整LV上的文件系统。
extend lv和reduce lv中介绍了几种文件系统的设置方法。
lv device file missing
lvs可以看到lv，当时/dev/mapper中没有对应的设备文件。
lvm
lvm> vgscan ## scan for volume groups
lvm> vgchange -a y ## activates the volume groups
参考
