逻辑卷管理器
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LVM（Logical Volume Manager，逻辑卷管理器）是动态划分磁盘分区的工具，它在硬盘分区和文件系统之间添加了一个逻辑层，可以让磁盘分区容量调整变得简单而高效。使用LVM可以动态的增加/缩小LVM磁盘分区的容量而不会破坏数据。
物理卷（Physical Volume，PV）可以是单独磁盘，也可以是磁盘分区或RAID磁盘阵列。
卷组（Volume Group，VG）PV的组合，VG可以看作单独的逻辑磁盘。
逻辑卷（Logical Volume，LV）逻辑上的分区。
PE（Physical Extent）：物理卷被划分为称为PE的基本单元，具有唯一编号的PE是可以被LVM寻址的最小单元。PE大小可配置，默认为4MB。
LE（Logical Extent）：逻辑卷被划分为称为LE的可寻址的基本单元，在同一卷组中，LE的大小和PE的大小是相同的，并且一一对应。
新建逻辑卷
1. 准备两块新硬盘设备
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 20G 0 disk
├─sda1 8:1 0 1G 0 part /boot
└─sda2 8:2 0 19G 0 part
├─rhel-root 253:0 0 17G 0 lvm /
└─rhel-swap 253:1 0 2G 0 lvm [SWAP]
sdb 8:16 0 20G 0 disk
sdc 8:32 0 20G 0 disk
sr0 11:0 1 4.2G 0 rom /run/media/root/RHEL-7.6 Server.x86_64
2. 首先对物理磁盘做PV声明（在物理层做事儿）——让新添加的两块硬盘设备支持LVM技术
[root@promote ~]# pvcreate /dev/sdb /dev/sdc
Physical volume "/dev/sdb" successfully created.
Physical volume "/dev/sdc" successfully created.
3. 将物理卷融合成一个新的逻辑磁盘——卷组
将两块硬盘设备加入到myVG卷组
[root@promote ~]# vgcreate myVG /dev/sdb /dev/sdc
Volume group "myVG" successfully created
查看卷组状态
[root@promote ~]# vgcreate myVG /dev/sdb /dev/sdc
Volume group "myVG" successfully created
[root@promote ~]#
[root@promote ~]#
[root@promote ~]# vgdisplay
--- Volume group ---
VG Name rhel
System ID
Format lvm2
Metadata Areas 1
Metadata Sequence No 3
VG Access read/write
VG Status resizable
MAX LV 0
Cur LV 2
Open LV 2
Max PV 0
Cur PV 1
Act PV 1
VG Size <19.00 GiB
PE Size 4.00 MiB
Total PE 4863
Alloc PE / Size 4863 / <19.00 GiB
Free PE / Size 0 / 0
VG UUID FxGwXE-2slI-Mk1r-3Dfe-EqUq-MkMK-MyPerA
--- Volume group ---
VG Name myVG
System ID
Format lvm2
Metadata Areas 2
Metadata Sequence No 1
VG Access read/write
VG Status resizable
MAX LV 0
Cur LV 0
Open LV 0
Max PV 0
Cur PV 2
Act PV 2
VG Size 39.99 GiB
PE Size 4.00 MiB
Total PE 10238
Alloc PE / Size 0 / 0
Free PE / Size 10238 / 39.99 GiB
VG UUID AeQ4hc-OBVg-yPBO-Sw1b-o1sr-vehG-lntDPV
4. 对卷组进行分区形成逻辑卷（在LVM软件内操作）
切割出一个100MB的的逻辑卷设备。对逻辑卷切割时有两种计量单位，第一种以容量为单位，所使用参数为 -L ；另一种以基本单元的个数为单位，使用的参数是-l。
[root@promote ~]# lvcreate -n lv0 -L 100M myVG
Logical volume "lv0" created.
[root@promote ~]# lvdisplay
--- Logical volume ---
LV Path /dev/rhel/root
LV Name root
VG Name rhel
LV UUID WYj3d9-IIEq-f1HK-K2Y6-t4R6-5bwn-JJShp4
LV Write Access read/write
LV Creation host, time localhost, 2020-03-24 19:55:51 +0800
LV Status available
# open 1
LV Size <17.00 GiB
Current LE 4351
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 8192
Block device 253:0
--- Logical volume ---
LV Path /dev/rhel/swap
LV Name swap
VG Name rhel
LV UUID 0mj0nq-qLDj-r8CM-Ftr8-NQTJ-uX6O-yW3QI9
LV Write Access read/write
LV Creation host, time localhost, 2020-03-24 19:55:51 +0800
LV Status available
# open 2
LV Size 2.00 GiB
Current LE 512
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 8192
Block device 253:1
--- Logical volume ---
LV Path /dev/myVG/lv0
LV Name lv0
VG Name myVG
LV UUID h0Ko7Q-t20v-iZfq-zObG-rc21-uMCK-3R2tHI
LV Write Access read/write
LV Creation host, time promote.cache-dns.local, 2020-04-18 11:39:13 +0800
LV Status available
# open 0
LV Size 100.00 MiB
Current LE 25
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 8192
Block device 253:2
5. 格式化逻辑卷并挂载到相应目录
[root@promote ~]# mkfs.ext4 /dev/myVG/lv0
mke2fs 1.42.9 (28-Dec-2013)
Filesystem label=
OS type: Linux
Block size=1024 (log=0)
Fragment size=1024 (log=0)
Stride=0 blocks, Stripe width=0 blocks
25688 inodes, 102400 blocks
5120 blocks (5.00%) reserved for the super user
First data block=1
Maximum filesystem blocks=33685504
13 block groups
8192 blocks per group, 8192 fragments per group
1976 inodes per group
Superblock backups stored on blocks:
8193, 24577, 40961, 57345, 73729
Allocating group tables: done
Writing inode tables: done
Creating journal (4096 blocks): done
Writing superblocks and filesystem accounting information: done
[root@promote ~]#
[root@promote ~]#
[root@promote ~]#
[root@promote ~]# mkdir /lv0
[root@promote ~]# echo "/dev/myVG/lv0 /lv0 ext4 defaults 0 0" >> /etc/fstab
[root@promote ~]# mount -a
[root@promote ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/rhel-root 17G 8.6G 8.4G 51% /
devtmpfs 894M 0 894M 0% /dev
tmpfs 910M 0 910M 0% /dev/shm
tmpfs 910M 11M 900M 2% /run
tmpfs 910M 0 910M 0% /sys/fs/cgroup
/dev/sda1 1014M 178M 837M 18% /boot
tmpfs 182M 4.0K 182M 1% /run/user/42
tmpfs 182M 28K 182M 1% /run/user/0
/dev/sr0 4.2G 4.2G 0 100% /run/media/root/RHEL-7.6 Server.x86_64
/dev/mapper/myVG-lv0 93M 1.6M 85M 2% /lv0
扩容逻辑卷（扩容前一定先卸载设备与挂载点的关联）
1. 卸载
[root@promote ~]# umount /lv0
2. 扩展逻辑卷至300M
[root@promote ~]# lvextend -L 300M /dev/myVG/lv0
Size of logical volume myVG/lv0 changed from 100.00 MiB (25 extents) to 300.00 MiB (75 extents).
Logical volume myVG/lv0 successfully resized.
3. 检查硬盘完整性并重置硬盘容量
[root@promote ~]# e2fsck -f /dev/myVG/lv0
e2fsck 1.42.9 (28-Dec-2013)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
/dev/myVG/lv0: 11/25688 files (9.1% non-contiguous), 8896/102400 blocks
[root@promote ~]# resize2fs /dev/myVG/lv0
resize2fs 1.42.9 (28-Dec-2013)
Resizing the filesystem on /dev/myVG/lv0 to 307200 (1k) blocks.
The filesystem on /dev/myVG/lv0 is now 307200 blocks long.
4.重新挂载硬盘设备并查看挂载状态
[root@promote ~]# mount -a
[root@promote ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/rhel-root 17G 8.6G 8.4G 51% /
devtmpfs 894M 0 894M 0% /dev
tmpfs 910M 0 910M 0% /dev/shm
tmpfs 910M 11M 900M 2% /run
tmpfs 910M 0 910M 0% /sys/fs/cgroup
/dev/sda1 1014M 178M 837M 18% /boot
tmpfs 182M 4.0K 182M 1% /run/user/42
tmpfs 182M 28K 182M 1% /run/user/0
/dev/sr0 4.2G 4.2G 0 100% /run/media/root/RHEL-7.6 Server.x86_64
/dev/mapper/myVG-lv0 287M 2.0M 266M 1% /lv0
缩小逻辑卷
相较于扩容，缩小逻辑卷数据丢失的风险更大，因此要提前备份数据。Linux系统规定，在进行LVM缩容操作之前，需要检查文件系统的完整性。
1. 卸载文件系统
[root@promote ~]# umount /lv0
2. 检查文件系统的完整性
[root@promote ~]# e2fsck -f /dev/myVG/lv0
e2fsck 1.42.9 (28-Dec-2013)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
/dev/myVG/lv0: 11/75088 files (9.1% non-contiguous), 15637/307200 blocks
3. 缩小逻辑卷容量（必须首先缩小逻辑卷的逻辑边界，再缩小物理边界）
[root@promote ~]# resize2fs /dev/m
mapper/ mcelog mem midi mqueue/ myVG/
[root@promote ~]# resize2fs /dev/myVG/lv0 100M
resize2fs 1.42.9 (28-Dec-2013)
Resizing the filesystem on /dev/myVG/lv0 to 102400 (1k) blocks.
The filesystem on /dev/myVG/lv0 is now 102400 blocks long.
[root@promote ~]# lvreduce -L 100M /dev/myVG/lv0
WARNING: Reducing active logical volume to 100.00 MiB.
THIS MAY DESTROY YOUR DATA (filesystem etc.)
Do you really want to reduce myVG/lv0? [y/n]: y
Size of logical volume myVG/lv0 changed from 300.00 MiB (75 extents) to 100.00 MiB (25 extents).
Logical volume myVG/lv0 successfully resized.
4. 重新挂载并查看挂载状态
[root@promote ~]# mount -a
[root@promote ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/rhel-root 17G 8.6G 8.4G 51% /
devtmpfs 894M 0 894M 0% /dev
tmpfs 910M 0 910M 0% /dev/shm
tmpfs 910M 11M 900M 2% /run
tmpfs 910M 0 910M 0% /sys/fs/cgroup
/dev/sda1 1014M 178M 837M 18% /boot
tmpfs 182M 4.0K 182M 1% /run/user/42
tmpfs 182M 28K 182M 1% /run/user/0
/dev/sr0 4.2G 4.2G 0 100% /run/media/root/RHEL-7.6 Server.x86_64
/dev/mapper/myVG-lv0 93M 1.6M 85M 2% /lv0
逻辑卷快照
LVM的快照卷功能的两个特点
- 快照卷的容量必须等同于逻辑卷的容量；
- 快照卷仅一次有效，一旦执行还原操作后会被立即自动删除。
1. 向逻辑卷lv0所挂载的目录中写入一个文件
[root@promote ~]# echo "Hello, World" > /lv0/readme.txt
[root@promote ~]# ls /lv0
lost+found readme.txt
2. 使用-s参数生成一个快照卷，使用-L 参数指定切割的大小，并在命令后写上针对的逻辑卷
[root@promote ~]# lvcreate -L 100M -s -n SNAP /dev/myVG/lv0
Logical volume "SNAP" created.
[root@promote ~]# lvdisplay
--- Logical volume ---
LV Path /dev/rhel/root
LV Name root
VG Name rhel
LV UUID WYj3d9-IIEq-f1HK-K2Y6-t4R6-5bwn-JJShp4
LV Write Access read/write
LV Creation host, time localhost, 2020-03-24 19:55:51 +0800
LV Status available
# open 1
LV Size <17.00 GiB
Current LE 4351
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 8192
Block device 253:0
--- Logical volume ---
LV Path /dev/rhel/swap
LV Name swap
VG Name rhel
LV UUID 0mj0nq-qLDj-r8CM-Ftr8-NQTJ-uX6O-yW3QI9
LV Write Access read/write
LV Creation host, time localhost, 2020-03-24 19:55:51 +0800
LV Status available
# open 2
LV Size 2.00 GiB
Current LE 512
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 8192
Block device 253:1
--- Logical volume ---
LV Path /dev/myVG/lv0
LV Name lv0
VG Name myVG
LV UUID h0Ko7Q-t20v-iZfq-zObG-rc21-uMCK-3R2tHI
LV Write Access read/write
LV Creation host, time promote.cache-dns.local, 2020-04-18 11:39:13 +0800
LV snapshot status source of
SNAP [active]
LV Status available
# open 1
LV Size 100.00 MiB
Current LE 25
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 8192
Block device 253:2
--- Logical volume ---
LV Path /dev/myVG/SNAP
LV Name SNAP
VG Name myVG
LV UUID vs61AA-nHnS-QxxE-Aclj-nB8x-32lY-0dlFM7
LV Write Access read/write
LV Creation host, time promote.cache-dns.local, 2020-04-18 12:01:00 +0800
LV snapshot status active destination for lv0
LV Status available
# open 0
LV Size 100.00 MiB
Current LE 25
COW-table size 100.00 MiB
COW-table LE 25
Allocated to snapshot 0.01%
Snapshot chunk size 4.00 KiB
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 8192
Block device 253:5
3. 在逻辑卷lv0所挂载目录中创建一个100MB的垃圾文件，查看快照卷状态发现存储空间所占用量上升
[root@promote ~]# dd if=/dev/zero of=/lv0/files count=1 bs=100M
dd: error writing ‘/lv0/files’: No space left on device
1+0 records in
0+0 records out
93646848 bytes (94 MB) copied, 3.25314 s, 28.8 MB/s
[root@promote ~]# lvdisplay
--- Logical volume ---
LV Path /dev/rhel/root
LV Name root
VG Name rhel
LV UUID WYj3d9-IIEq-f1HK-K2Y6-t4R6-5bwn-JJShp4
LV Write Access read/write
LV Creation host, time localhost, 2020-03-24 19:55:51 +0800
LV Status available
# open 1
LV Size <17.00 GiB
Current LE 4351
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 8192
Block device 253:0
--- Logical volume ---
LV Path /dev/rhel/swap
LV Name swap
VG Name rhel
LV UUID 0mj0nq-qLDj-r8CM-Ftr8-NQTJ-uX6O-yW3QI9
LV Write Access read/write
LV Creation host, time localhost, 2020-03-24 19:55:51 +0800
LV Status available
# open 2
LV Size 2.00 GiB
Current LE 512
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 8192
Block device 253:1
--- Logical volume ---
LV Path /dev/myVG/lv0
LV Name lv0
VG Name myVG
LV UUID h0Ko7Q-t20v-iZfq-zObG-rc21-uMCK-3R2tHI
LV Write Access read/write
LV Creation host, time promote.cache-dns.local, 2020-04-18 11:39:13 +0800
LV snapshot status source of
SNAP [active]
LV Status available
# open 1
LV Size 100.00 MiB
Current LE 25
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 8192
Block device 253:2
--- Logical volume ---
LV Path /dev/myVG/SNAP
LV Name SNAP
VG Name myVG
LV UUID vs61AA-nHnS-QxxE-Aclj-nB8x-32lY-0dlFM7
LV Write Access read/write
LV Creation host, time promote.cache-dns.local, 2020-04-18 12:01:00 +0800
LV snapshot status active destination for lv0
LV Status available
# open 0
LV Size 100.00 MiB
Current LE 25
COW-table size 100.00 MiB
COW-table LE 25
Allocated to snapshot 89.79%
Snapshot chunk size 4.00 KiB
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 8192
Block device 253:5
4. 对逻辑卷进行快照还原操作（先卸载逻辑卷设备与目录的挂载）
root@promote ~]# umount /lv0
[root@promote ~]# lvconvert --merge /dev/myVG/SNAP
Merging of volume myVG/SNAP started.
myVG/lv0: Merged: 92.96%
5. 挂载并查看
[root@promote ~]# mount -a
[root@promote ~]# ls /lv0
lost+found readme.txt
删除逻辑卷
1. 取消逻辑卷与目录的挂载关联，删除配置文件中永久生效的设备参数
[root@promote ~]# umount /lv0
2. 删除逻辑卷设备
root@promote ~]# lvremove /dev/myVG/lv0
Do you really want to remove active logical volume myVG/lv0? [y/n]: y
Logical volume "lv0" successfully removed
3. 删除卷组
[root@promote ~]# vgremove myVG
Volume group "myVG" successfully removed
4. 删除物理卷设备
[root@promote ~]# pvremove /dev/sdb /dev/sdc
Labels on physical volume "/dev/sdb" successfully wiped.
Labels on physical volume "/dev/sdc" successfully wiped.
注意点：
- 使用LVM的前提是安装了一个LVM的软件。
- 最底层必须是物理存储设备（一个及以上多个磁盘、分区或RAID磁盘阵列组成），因为是将底层设备在LVM软件中做了二次分配，动态进行扩容、缩容操作（文件系统不同操作不同，如ext文件系统可以支持扩容缩容操作，xfs文件系统只能做缩容操作）
- /boot分区不可以是逻辑卷，因为装载程序无法读取逻辑卷。
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