1. 理解LVM工作原理
什么是LVM？
LVM是逻辑盘卷管理（Logical Volume Manager）的简称，它是Linux环境下对磁盘分区进行管理的一种机制，LVM是建立在硬盘和分区之上的一个逻辑层，来提高磁盘分区管理的灵活性。
为什么要使用LVM？
在日常工作或者学习中，随着电脑的不断被使用，我们的磁盘空间可能会越来越小，这时候，我们不能直接更换大硬盘，因为硬盘有价，数据无价，这时候我们就可以使用LVM，LVM将存储虚拟化,使用逻辑卷,你不会受限于物理磁盘的大小,另外,和硬件相关的存储设置被其隐藏,你能不用停止应用或卸载文件系统来调整卷大小或数据迁移.这样能减少操作成本，LVM最大的特点就是可以对磁盘进行动态管理。因为逻辑卷的大小是可以动态调整的，而且不会丢失现有的数据。如果我们新增加了硬盘，其也不会改变现有上层的逻辑卷。作为一个动态磁盘管理机制，逻辑卷技术大大提高了磁盘管理的灵活性。
LVM工作机制？
LVM就是通过将底层的物理硬盘抽象的封装起来，然后以逻辑卷的方式呈现给上层应用。在传统的磁盘管理机制中，我们的上层应用是直接访问文件系统，从而对底层的物理硬盘进行读取，而在LVM中，其通过对底层的硬盘进行封装，当我们对底层的物理硬盘进行操作时，其不再是针对于分区进行操作，而是通过一个叫做逻辑卷的东西来对其进行底层的磁盘管理操作。
逻辑卷管理概念？
物理卷（PV, Physical Volume）
物理卷就是指磁盘,磁盘分区或从逻辑上和磁盘分区具有同样功能的设备(如RAID)，是LVM的基本存储逻辑块，但和基本的物理存储介质（如分区、磁盘等）比较，却包含有和LVM相关的管理参数。当前LVM允许你在每个物理卷上保存这个物理卷的0至2份元数据拷贝.默认为1,保存在设备的开始处.为2时,在设备结束处保存第二份备份.
卷组（VG, Volume Group）
LVM卷组类似于非LVM系统中的物理硬盘，其由物理卷组成。能在卷组上创建一个或多个“LVM分区”（逻辑卷），LVM卷组由一个或多个物理卷组成。
逻辑卷（LV, Logical Volume）
LVM的逻辑卷类似于非LVM系统中的硬盘分区，在逻辑卷之上能建立文件系统(比如/home或/usr等)。
LVM原理图
2. LVM操作案例分析
添加磁盘并创建一个分区
[root@localhost ~]# fdisk -l //查看磁盘情况 [root@localhost ~]# fdisk /dev/sdb //进入磁盘（可以依次按键n-->e-->回车-->回车-->w,即用此磁盘空闲空间创建分区） Welcome to fdisk (util-linux 2.23.2). Changes will remain in memory only, until you decide to write them. Be careful before using the write command. Device does not contain a recognized partition table Building a new DOS disklabel with disk identifier 0xeed8cf69. Command (m for help): p //查看分区列表 Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk label type: dos Disk identifier: 0xeed8cf69 Device Boot Start End Blocks Id System Command (m for help): n //添加一个分区 Partition type: p primary (0 primary, 0 extended, 4 free) e extended Select (default p): Using default response p Partition number (1-4, default 1): +20G Partition number (1-4, default 1): First sector (2048-104857599, default 2048): Using default value 2048 Last sector, +sectors or +size{K,M,G} (2048-104857599, default 104857599): +20G Partition 1 of type Linux and of size 20 GiB is set Command (m for help): t //更改分区类型 Selected partition 1 Hex code (type L to list all codes): l //分区类型列表 Hex code (type L to list all codes): 8e //将新添加的分区标注成LVM,只要是‘8e’(LVM)类型的磁盘分区都可以用来扩展卷组。 Changed type of partition 'Linux' to 'Linux LVM' Command (m for help): p //查看分区表 Disk /dev/sdb: 53.7 GB, 53687091200 bytes, 104857600 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk label type: dos Disk identifier: 0xeed8cf69 Device Boot Start End Blocks Id System /dev/sdb1 2048 41945087 20971520 8e Linux LVM Command (m for help): w //保存 The partition table has been altered! Calling ioctl() to re-read partition table. Syncing disks.
创建逻辑卷lv01并挂载到/lvm01目录上。
[root@localhost ~]# pvcreate /dev/sdb1 //创建物理卷 Physical volume "/dev/sdb1" successfully created [root@localhost ~]# mkfs.ext4 /dev/sdb1 //格式化新添加的分区 mke2fs 1.42.9 (28-Dec-2013) Filesystem label= OS type: Linux Block size=4096 (log=2) Fragment size=4096 (log=2) Stride=0 blocks, Stripe width=0 blocks 1310720 inodes, 5242880 blocks 262144 blocks (5.00%) reserved for the super user First data block=0 Maximum filesystem blocks=2153775104 160 block groups 32768 blocks per group, 32768 fragments per group 8192 inodes per group Superblock backups stored on blocks: 32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 4096000 Allocating group tables: done Writing inode tables: done Creating journal (32768 blocks): done Writing superblocks and filesystem accounting information: done [root@localhost ~]# pvcreate /dev/sdb1 //创建pv WARNING: ext4 signature detected on /dev/sdb1 at offset 1080. Wipe it? [y/n]: y Wiping ext4 signature on /dev/sdb1. Physical volume "/dev/sdb1" successfully created [root@localhost ~]# pvdisplay /dev/sdb1 //查看pv信息 "/dev/sdb1" is a new physical volume of "20.00 GiB" --- NEW Physical volume --- PV Name /dev/sdb1 VG Name PV Size 20.00 GiB Allocatable NO PE Size 0 Total PE 0 Free PE 0 Allocated PE 0 PV UUID cL1S1N-nUGj-DuYa-9RP0-ened-A4ZZ-FTlOWX [root@localhost ~]# vgcreate vg01 /dev/sdb1 Volume group "vg01" successfully created [root@localhost ~]# vgdisplay vg01 --- Volume group --- VG Name vg01 System ID Format lvm2 Metadata Areas 1 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 1 Act PV 1 VG Size 20.00 GiB PE Size 4.00 MiB Total PE 5119 Alloc PE / Size 0 / 0 Free PE / Size 5119 / 20.00 GiB VG UUID lghbtI-4usq-GFEj-Zr26-7NrP-UUE3-0RHMF5 [root@localhost ~]# lvcreate -L 10M -n lv01 vg01 //从卷组vg01中创建一个大小为10M名字为lv01的逻辑卷， 如果要使用卷组剩下的所有空间创建逻辑卷 lvcreate -n lv-name -l 100%FREE vg-name Rounding up size to full physical extent 12.00 MiB Logical volume "lv01" created. [root@localhost ~]# lvdisplay vg01 //查看在vg01组创建的逻辑卷 --- Logical volume --- LV Path /dev/vg01/lv01 LV Name lv01 VG Name vg01 LV UUID A1CBRX-wLOF-2d7D-SPvg-sBhD-3wzO-WtbmeH LV Write Access read/write LV Creation host, time localhost.localdomain, 2020-01-14 17:08:48 +0800 LV Status available # open 0 LV Size 12.00 MiB Current LE 3 Segments 1 Allocation inherit Read ahead sectors auto - currently set to 8192 Block device 253:3 [root@localhost ~]# mkfs.ext4 /dev/vg01/lv01 //逻辑卷已经准备好了，我们可以格式化和挂载逻辑卷，就像其它ext2/3/4分区一样！ 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 3072 inodes, 12288 blocks 614 blocks (5.00%) reserved for the super user First data block=1 Maximum filesystem blocks=12582912 2 block groups 8192 blocks per group, 8192 fragments per group 1536 inodes per group Superblock backups stored on blocks: 8193 Allocating group tables: done Writing inode tables: done Creating journal (1024 blocks): done Writing superblocks and filesystem accounting information: done [root@localhost ~]# mkdir /lvm01 [root@localhost ~]# mount /dev/vg01/lv01 /lvm01/ [root@localhost ~]# df -h Filesystem Size Used Avail Use% Mounted on /dev/mapper/centos-root 50G 845M 50G 2% / devtmpfs 3.9G 0 3.9G 0% /dev tmpfs 3.9G 0 3.9G 0% /dev/shm tmpfs 3.9G 8.6M 3.9G 1% /run tmpfs 3.9G 0 3.9G 0% /sys/fs/cgroup /dev/mapper/centos-home 42G 33M 42G 1% /home /dev/sda1 497M 123M 375M 25% /boot tmpfs 781M 0 781M 0% /run/user/0 /dev/mapper/vg01-lv01 11M 204K 9.6M 3% /lvm01
扩展LVM空间
逻辑卷lv01只有16MB的空间，我们需要对其进行扩展空间，扩展空间并不会影响到之前存储的数据。
实际情景1：卷组vg01有空闲的空间，直接进行扩展就可以。
[root@localhost ~]# lvextend -L +200M /dev/vg01/lv01 //使用lvextend命令直接对逻辑卷进行扩展200M Size of logical volume vg01/lv01 changed from 52.00 MiB (13 extents) to 252.00 MiB (63 extents). Logical volume lv01 successfully resized. [root@localhost ~]# df -Th //发现分区大小并没有改变 Filesystem Type Size Used Avail Use% Mounted on /dev/mapper/centos-root xfs 50G 845M 50G 2% / devtmpfs devtmpfs 3.9G 0 3.9G 0% /dev tmpfs tmpfs 3.9G 0 3.9G 0% /dev/shm tmpfs tmpfs 3.9G 8.6M 3.9G 1% /run tmpfs tmpfs 3.9G 0 3.9G 0% /sys/fs/cgroup /dev/mapper/centos-home xfs 42G 33M 42G 1% /home /dev/sda1 xfs 497M 123M 375M 25% /boot tmpfs tmpfs 781M 0 781M 0% /run/user/0 /dev/mapper/vg01-lv01 ext4 50M 396K 46M 1% /lvm01 [root@localhost ~]# resize2fs /dev/vg01/lv01 //激活 resize2fs 1.42.9 (28-Dec-2013) Filesystem at /dev/vg01/lv01 is mounted on /lvm01; on-line resizing required old_desc_blocks = 1, new_desc_blocks = 2 The filesystem on /dev/vg01/lv01 is now 258048 blocks long. [root@localhost ~]# df -Th //可以看到/lvm01正常了 Filesystem Type Size Used Avail Use% Mounted on /dev/mapper/centos-root xfs 50G 845M 50G 2% / devtmpfs devtmpfs 3.9G 0 3.9G 0% /dev tmpfs tmpfs 3.9G 0 3.9G 0% /dev/shm tmpfs tmpfs 3.9G 8.6M 3.9G 1% /run tmpfs tmpfs 3.9G 0 3.9G 0% /sys/fs/cgroup /dev/mapper/centos-home xfs 42G 33M 42G 1% /home /dev/sda1 xfs 497M 123M 375M 25% /boot tmpfs tmpfs 781M 0 781M 0% /run/user/0 /dev/mapper/vg01-lv01 ext4 245M 768K 233M 1% /lvm01
实际情景2：卷组vg01空间不足，先扩展vg，扩展vg就是往vg中加pv
使用fdisk命令创建一个分区
[root@localhost ~]# fdisk /dev/sdc Command (m for help): n Partition type: p primary (0 primary, 0 extended, 4 free) e extended Select (default p): Hex code (type L to list all codes): 8e Changed type of partition 'Linux' to 'Linux LVM' Command (m for help): w The partition table has been altered! Calling ioctl() to re-read partition table. Syncing disks. [root@localhost ~]# fdisk /dev/sdc Welcome to fdisk (util-linux 2.23.2). Changes will remain in memory only, until you decide to write them. Be careful before using the write command. Command (m for help): p Disk /dev/sdc: 85.9 GB, 85899345920 bytes, 167772160 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk label type: dos Disk identifier: 0xeeb944e3 Device Boot Start End Blocks Id System /dev/sdc1 2048 167772159 83885056 8e Linux LVM
添加物理卷并添加到卷组vg01中，然后再进行逻辑卷扩容操作
[root@localhost ~]# pvcreate /dev/sdc1 //创建物理卷 Physical volume "/dev/sdc1" successfully created [root@localhost ~]# mkfs.ext4 /dev/sdc1 mke2fs 1.42.9 (28-Dec-2013) Filesystem label= OS type: Linux Block size=4096 (log=2) Fragment size=4096 (log=2) Stride=0 blocks, Stripe width=0 blocks 5242880 inodes, 20971264 blocks 1048563 blocks (5.00%) reserved for the super user First data block=0 Maximum filesystem blocks=2168455168 640 block groups 32768 blocks per group, 32768 fragments per group 8192 inodes per group Superblock backups stored on blocks: 32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 4096000, 7962624, 11239424, 20480000 Allocating group tables: done Writing inode tables: done Creating journal (32768 blocks): done Writing superblocks and filesystem accounting information: done [root@localhost ~]# mkfs.ext4 /dev/sdc1 mke2fs 1.42.9 (28-Dec-2013) Filesystem label= OS type: Linux Block size=4096 (log=2) Fragment size=4096 (log=2) Stride=0 blocks, Stripe width=0 blocks 5242880 inodes, 20971264 blocks 1048563 blocks (5.00%) reserved for the super user First data block=0 Maximum filesystem blocks=2168455168 640 block groups 32768 blocks per group, 32768 fragments per group 8192 inodes per group Superblock backups stored on blocks: 32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 4096000, 7962624, 11239424, 20480000 Allocating group tables: done Writing inode tables: done Creating journal (32768 blocks): done Writing superblocks and filesystem accounting information: done [root@localhost ~]# vgextend vg01 /dev/sdc1 //将物理卷/dev/sdc1添加到vg01卷组里面 WARNING: ext4 signature detected on /dev/sdc1 at offset 1080. Wipe it? [y/n]: y Wiping ext4 signature on /dev/sdc1. Physical volume "/dev/sdc1" successfully created Volume group "vg01" successfully extended [root@localhost ~]# lvextend -L +15G /dev/vg01/lv02 //扩容 Size of logical volume vg01/lv02 changed from 19.75 GiB (5056 extents) to 34.75 GiB (8896 extents). Logical volume lv02 successfully resized. [root@localhost ~]# resize2fs /dev/vg01/lv02 resize2fs 1.42.9 (28-Dec-2013) Filesystem at /dev/vg01/lv02 is mounted on /lvm02; on-line resizing required old_desc_blocks = 3, new_desc_blocks = 5 The filesystem on /dev/vg01/lv02 is now 9109504 blocks long. [root@localhost ~]# df -h Filesystem Size Used Avail Use% Mounted on /dev/mapper/centos-root 50G 845M 50G 2% / devtmpfs 3.9G 0 3.9G 0% /dev tmpfs 3.9G 0 3.9G 0% /dev/shm tmpfs 3.9G 8.6M 3.9G 1% /run tmpfs 3.9G 0 3.9G 0% /sys/fs/cgroup /dev/mapper/centos-home 42G 33M 42G 1% /home /dev/sda1 497M 123M 375M 25% /boot tmpfs 781M 0 781M 0% /run/user/0 /dev/mapper/vg01-lv01 245M 768K 233M 1% /lvm01 /dev/mapper/vg01-lv02 35G 48M 33G 1% /lvm0
缩小逻辑卷
相较于扩容逻辑卷，在对逻辑卷进行缩容操作时，其丢失数据的风险更大。所以在生产环境中执行相应操作时，一定要提前备份好数据。另外Linux系统规定，在对LVM逻辑卷进行缩容操作之前，要先检查文件系统的完整性（当然这也是为了保证我们的数据安全）。在执行缩容操作前记得先把文件系统卸载掉。
第一步：卸载文件系统
[root@localhost ~]# df -Th Filesystem Type Size Used Avail Use% Mounted on devtmpfs devtmpfs 3.8G 0 3.8G 0% /dev tmpfs tmpfs 3.9G 276K 3.9G 1% /dev/shm tmpfs tmpfs 3.9G 12M 3.8G 1% /run tmpfs tmpfs 3.9G 0 3.9G 0% /sys/fs/cgroup /dev/mapper/centos-root xfs 19G 2.8G 16G 15% / /dev/sda1 xfs 497M 168M 329M 34% /boot tmpfs tmpfs 781M 0 781M 0% /run/user/0 /dev/mapper/vg1-lv1 ext4 93M 1.6M 85M 2% /data [root@localhost ~]# umount /data
第二步：检查文件系统的完整性。
[root@localhost ~]# e2fsck -f /dev/vg1/lv1 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/vg1/lv1: 11/25688 files (9.1% non-contiguous), 8896/102400 blocks
第三步：把逻辑卷缩小到50M
[root@localhost ~]# resize2fs /dev/vg1/lv1 50M resize2fs 1.42.9 (28-Dec-2013) Resizing the filesystem on /dev/vg1/lv1 to 51200 (1k) blocks. The filesystem on /dev/vg1/lv1 is now 51200 blocks long. [root@localhost ~]# lvreduce -L 50M /dev/vg1/lv1 Rounding size to boundary between physical extents: 52.00 MiB. WARNING: Reducing active logical volume to 52.00 MiB. THIS MAY DESTROY YOUR DATA (filesystem etc.) Do you really want to reduce vg1/lv1? [y/n]: y Size of logical volume vg1/lv1 changed from 100.00 MiB (25 extents) to 52.00 MiB (13 extents). Logical volume vg1/lv1 successfully resized.
第四步：重新挂载逻辑卷
[root@localhost ~]# mount /dev/vg1/lv1 /data [root@localhost ~]# df -Th Filesystem Type Size Used Avail Use% Mounted on devtmpfs devtmpfs 3.8G 0 3.8G 0% /dev tmpfs tmpfs 3.9G 300K 3.9G 1% /dev/shm tmpfs tmpfs 3.9G 12M 3.8G 1% /run tmpfs tmpfs 3.9G 0 3.9G 0% /sys/fs/cgroup /dev/mapper/centos-root xfs 19G 2.8G 16G 15% / /dev/sda1 xfs 497M 168M 329M 34% /boot tmpfs tmpfs 781M 0 781M 0% /run/user/0 /dev/mapper/vg1-lv1 ext4 45M 1.1M 40M 3% /data
第五步：设置开启自动挂载
[root@localhost ~]# blkid /dev/sda1: UUID="d9692c2f-a923-4ad0-bec4-6dd857bd3605" TYPE="xfs" /dev/sda2: UUID="7ohdUl-beCh-ld4I-5aET-kpfI-36DU-H0Ocfv" TYPE="LVM2_member" /dev/sdb5: UUID="MrqzV2-0RWe-obBo-90XK-BuGX-p9og-CjNUPJ" TYPE="LVM2_member" /dev/mapper/centos-root: UUID="f8cc13e4-cab2-45a4-8405-a32f8d0954d0" TYPE="xfs" /dev/mapper/centos-swap: UUID="bbbe0095-76b6-4c3c-9f91-7592b3437b5a" TYPE="swap" /dev/mapper/vg1-lv1: UUID="37ccb234-3952-4935-94ca-9468c10ade26" TYPE="ext4" /dev/sdb1: PTTYPE="dos" [root@localhost ~]# echo "UUID=37ccb234-3952-4935-94ca-9468c10ade26 /data ext4 defaults 0 0" >> /etc/fstab