1. 理解LVM工作原理
什么是LVM？
LVM是邏輯盤卷管理（Logical Volume Manager）的簡稱，它是Linux環境下對磁盤分區進行管理的一種機制，LVM是建立在硬盤和分區之上的一個邏輯層，來提高磁盤分區管理的靈活性。
為什么要使用LVM？
在日常工作或者學習中，隨着電腦的不斷被使用，我們的磁盤空間可能會越來越小，這時候，我們不能直接更換大硬盤，因為硬盤有價，數據無價，這時候我們就可以使用LVM，LVM將存儲虛擬化,使用邏輯卷,你不會受限於物理磁盤的大小,另外,和硬件相關的存儲設置被其隱藏,你能不用停止應用或卸載文件系統來調整卷大小或數據遷移.這樣能減少操作成本，LVM最大的特點就是可以對磁盤進行動態管理。因為邏輯卷的大小是可以動態調整的，而且不會丟失現有的數據。如果我們新增加了硬盤，其也不會改變現有上層的邏輯卷。作為一個動態磁盤管理機制，邏輯卷技術大大提高了磁盤管理的靈活性。
LVM工作機制？
LVM就是通過將底層的物理硬盤抽象的封裝起來，然后以邏輯卷的方式呈現給上層應用。在傳統的磁盤管理機制中，我們的上層應用是直接訪問文件系統，從而對底層的物理硬盤進行讀取，而在LVM中，其通過對底層的硬盤進行封裝，當我們對底層的物理硬盤進行操作時，其不再是針對於分區進行操作，而是通過一個叫做邏輯卷的東西來對其進行底層的磁盤管理操作。
邏輯卷管理概念？
物理卷（PV, Physical Volume）
物理卷就是指磁盤,磁盤分區或從邏輯上和磁盤分區具有同樣功能的設備(如RAID)，是LVM的基本存儲邏輯塊，但和基本的物理存儲介質（如分區、磁盤等）比較，卻包含有和LVM相關的管理參數。當前LVM允許你在每個物理卷上保存這個物理卷的0至2份元數據拷貝.默認為1,保存在設備的開始處.為2時,在設備結束處保存第二份備份.
卷組（VG, Volume Group）
LVM卷組類似於非LVM系統中的物理硬盤，其由物理卷組成。能在卷組上創建一個或多個“LVM分區”（邏輯卷），LVM卷組由一個或多個物理卷組成。
邏輯卷（LV, Logical Volume）
LVM的邏輯卷類似於非LVM系統中的硬盤分區，在邏輯卷之上能建立文件系統(比如/home或/usr等)。
LVM原理圖
2. LVM操作案例分析
添加磁盤並創建一個分區
[root@localhost ~]# fdisk -l //查看磁盤情況 [root@localhost ~]# fdisk /dev/sdb //進入磁盤（可以依次按鍵n-->e-->回車-->回車-->w,即用此磁盤空閑空間創建分區） 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 //查看分區列表 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 //添加一個分區 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 //更改分區類型 Selected partition 1 Hex code (type L to list all codes): l //分區類型列表 Hex code (type L to list all codes): 8e //將新添加的分區標注成LVM,只要是‘8e’(LVM)類型的磁盤分區都可以用來擴展卷組。 Changed type of partition 'Linux' to 'Linux LVM' Command (m for help): p //查看分區表 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.
創建邏輯卷lv01並掛載到/lvm01目錄上。
[root@localhost ~]# pvcreate /dev/sdb1 //創建物理卷 Physical volume "/dev/sdb1" successfully created [root@localhost ~]# mkfs.ext4 /dev/sdb1 //格式化新添加的分區 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 //創建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 //從卷組vg01中創建一個大小為10M名字為lv01的邏輯卷， 如果要使用卷組剩下的所有空間創建邏輯卷 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組創建的邏輯卷 --- 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 //邏輯卷已經准備好了，我們可以格式化和掛載邏輯卷，就像其它ext2/3/4分區一樣！ 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
擴展LVM空間
邏輯卷lv01只有16MB的空間，我們需要對其進行擴展空間，擴展空間並不會影響到之前存儲的數據。
實際情景1：卷組vg01有空閑的空間，直接進行擴展就可以。
[root@localhost ~]# lvextend -L +200M /dev/vg01/lv01 //使用lvextend命令直接對邏輯卷進行擴展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 //發現分區大小並沒有改變 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
實際情景2：卷組vg01空間不足，先擴展vg，擴展vg就是往vg中加pv
使用fdisk命令創建一個分區
[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
添加物理卷並添加到卷組vg01中，然后再進行邏輯卷擴容操作
[root@localhost ~]# pvcreate /dev/sdc1 //創建物理卷 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 //將物理卷/dev/sdc1添加到vg01卷組里面 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 //擴容 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
縮小邏輯卷
相較於擴容邏輯卷，在對邏輯卷進行縮容操作時，其丟失數據的風險更大。所以在生產環境中執行相應操作時，一定要提前備份好數據。另外Linux系統規定，在對LVM邏輯卷進行縮容操作之前，要先檢查文件系統的完整性（當然這也是為了保證我們的數據安全）。在執行縮容操作前記得先把文件系統卸載掉。
第一步：卸載文件系統
[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：檢查文件系統的完整性。
[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：把邏輯卷縮小到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：重新掛載邏輯卷
[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：設置開啟自動掛載
[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