LVM卷的创建及案例演示

LVM：Logical Volume Manager,  Version:2
dm： device mapper，将一个或多个底层块设备组织成一个逻辑设备的模块。
　　/dev/dm-#  这里的#表示数字，代表某一块dm设备
/dev/mapper/VG_NAME-LV_NAME
　　/dev/mapper/vol0-root
/dev/VG_NAME/LV_NAME
　　/dev/vol0/root

pv管理工具：
　　pvs：简要展示pv信息
　　pvdisplay：显示pv的详细信息
　　pvcreate /dev/DEVICE：创建pv
vg管理工具：
　　vgs
　　vgsdisplay
　　vgcreate  [-s #MG]  VolumeGroupName  PhysicalDevicePath [PhysicalDevicePath....]
　　vgextend  VolumnGroupName  PhysicalDevicePath  [PhysicalDevicePath...]
　　vgreduce  VolumnGroupName  PhysicalDevicePath  [PhysicalDevicePath...]
lv管理工具
　　lvs
　　lvdisplay
　　lvcreate  -L #[MG]  -n  LV_Name  VolumeGroup
扩展逻辑卷：
　　lvextend  -L [+]#[MGT] /dev/VG_NAME/LV_NAME
　　resize2fs  /dev/VG_NAME/LV_NAME
缩减逻辑卷
　　umount  /dev/VG_NAME/LV_NAME
　　e2fsck  -f  /dev/VG_NAME/LV_NAME                        #强制对磁盘进行检查坏块等错误。
　　resize2fs  /dev/VG_ANME/LV_NAME  #[MGT]
　　lvreduce  -L  [-]#[MGT] /dev/VG_NAME/LV_NAME
　　mount

看一下原理：

案例：我们讲解一个创建LVM卷

此时我安装一块1200G的硬盘，在Linux显示为/dev/xvdb的块设备。

[root@:vg_adn_clickhouseTest_3ubuntu:172.31.18.18 /dev]#fdisk /dev/xvdb

Welcome to fdisk (util-linux 2.31.1).
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/xvdb: 1.2 TiB, 1288490188800 bytes, 2516582400 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
Disklabel type: dos
Disk identifier: 0xc9629da1

Command (m for help): n
Partition type
   p   primary (0 primary, 0 extended, 4 free)
   e   extended (container for logical partitions)
Select (default p): p
Partition number (1-4, default 1):
First sector (2048-2516582399, default 2048):
Last sector, +sectors or +size{K,M,G,T,P} (2048-2516582399, default 2516582399): 

Created a new partition 1 of type 'Linux' and of size 1.2 TiB.
Partition #1 contains a LVM2_member signature.

Do you want to remove the signature? [Y]es/[N]o: Y

The signature will be removed by a write command.

Command (m for help): t
Selected partition 1
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@:vg_adn_clickhouseTest_3ubuntu:172.31.18.18 /dev]#ls
autofs           fd         log           mapper              ppp         tty50  tty6   ttyS2      vcs5   vga_arbiter
block            full       loop-control  mcelog              psaux       tty51  tty60  ttyS3      vcs6   vhost-net
btrfs-control    fuse       loop0         mem                 ptmx        tty52  tty61  ttyprintk  vcsa   vhost-vsock
char             hpet       loop1         memory_bandwidth    pts         tty53  tty62  uinput     vcsa1  xen
console          hugepages  loop2         mqueue              random      tty54  tty63  urandom    vcsa2  xvda
core             hwrng      loop3         net                 rfkill      tty55  tty7   vcs        vcsa3  xvda1
cpu_dma_latency  initctl    loop4         network_latency     rtc         tty56  tty8   vcs1       vcsa4  xvdb
cuse             input      loop5         network_throughput  rtc0        tty9   vcs2              vcsa5  xvdb1
disk             kmsg       loop6         null                shm         tty58  ttyS0  vcs3       vcsa6  zero
ecryptfs         lightnvm   loop7         port                snapshot    tty59  ttyS1  vcs4       vfio
[root@:vg_adn_clickhouseTest_3ubuntu:172.31.18.18 /dev]#pvcreate /dev/xvdb1
  Physical volume "/dev/xvdb1" successfully created.
[root@:vg_adn_clickhouseTest_3ubuntu:172.31.18.18 /dev]#pvdisplay
  "/dev/xvdb1" is a new physical volume of "1.17 TiB"
  --- NEW Physical volume ---
  PV Name               /dev/xvdb1
  VG Name
  PV Size               1.17 TiB
  Allocatable           NO
  PE Size               0
  Total PE              0
  Free PE               0
  Allocated PE          0
  PV UUID               u9Re6S-Bl6b-WLic-7aau-mOK5-2bBX-CB7TKg

[root@:vg_adn_clickhouseTest_3ubuntu:172.31.18.18 /dev]#vgcreate data /dev/xvdb1
  Volume group "data" successfully created
[root@:vg_adn_clickhouseTest_3ubuntu:172.31.18.18 /dev]#vgdisplay
  --- Volume group ---
  VG Name               data
  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               1.17 TiB
  PE Size               4.00 MiB
  Total PE              307199
  Alloc PE / Size       0 / 0
  Free  PE / Size       307199 / 1.17 TiB
  VG UUID               1zQAIi-3O6I-k0re-ZnpQ-9o16-ZG4i-zbiW5L

[root@:vg_adn_clickhouseTest_3ubuntu:172.31.18.18 /dev]#lvcreate -L 1170G -n lv-data data       #这里的lv-data是lvm的名字，是自定义的。而data是vgGroup的名称
  Logical volume "lv-data" created.
[root@:vg_adn_clickhouseTest_3ubuntu:172.31.18.18 /dev]#lvs
  LV      VG   Attr       LSize Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  lv-data data -wi-a----- 1.14t
[root@:vg_adn_clickhouseTest_3ubuntu:172.31.18.18 /dev]#lvdisplay
  --- Logical volume ---
  LV Path                /dev/data/lv-data
  LV Name                lv-data
  VG Name                data
  LV UUID                OtxncR-HT6N-filt-TM84-t19s-WaJg-3fbFws
  LV Write Access        read/write
  LV Creation host, time ip-172-31-18-18, 2018-12-21 11:48:03 +0800
  LV Status              available
  # open                 0
  LV Size                1.14 TiB
  Current LE             299520
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:0

我们已经创建好了卷，接下来就开始就开始格式化这个lvm卷才能使用。我一般格式化成ext4的文件系统的格式，最后再进行挂载即可。

[root@:vg_adn_clickhouseTest_3ubuntu:54.88.193.72:172.31.18.18 /dev]#mkfs -t ext4 /dev/mapper/data-lv--data
mke2fs 1.44.1 (24-Mar-2018)
Creating filesystem with 306708480 4k blocks and 76677120 inodes
Filesystem UUID: 48bfb718-44fc-4368-960c-d3b74dc7878a
Superblock backups stored on blocks:
    32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
    4096000, 7962624, 11239424, 20480000, 23887872, 71663616, 78675968,
    102400000, 214990848

Allocating group tables: done
Writing inode tables: done
Creating journal (262144 blocks): done
Writing superblocks and filesystem accounting information: done     

[root@:vg_adn_clickhouseTest_3ubuntu:54.88.193.72:172.31.18.18 /dev]#mkdir /data
[root@:vg_adn_clickhouseTest_3ubuntu:54.88.193.72:172.31.18.18 /dev]#cd /data
[root@:vg_adn_clickhouseTest_3ubuntu:54.88.193.72:172.31.18.18 /data]#ls[root@:vg_adn_clickhouseTest_3ubuntu:54.88.193.72:172.31.18.18 /data]#mount /dev/mapper/data-lv--data /data
[root@:vg_adn_clickhouseTest_3ubuntu:54.88.193.72:172.31.18.18 /data]#df -Th
Filesystem                Type      Size  Used Avail Use% Mounted on
udev                      devtmpfs   16G     0   16G   0% /dev
tmpfs                     tmpfs     3.2G  772K  3.2G   1% /run
/dev/xvda1                ext4       97G  1.6G   96G   2% /
tmpfs                     tmpfs      16G     0   16G   0% /dev/shm
tmpfs                     tmpfs     5.0M     0  5.0M   0% /run/lock
tmpfs                     tmpfs      16G     0   16G   0% /sys/fs/cgroup
/dev/loop0                squashfs   88M   88M     0 100% /snap/core/5328
/dev/loop1                squashfs   13M   13M     0 100% /snap/amazon-ssm-agent/495
tmpfs                     tmpfs     3.2G     0  3.2G   0% /run/user/1002
/dev/loop2                squashfs   90M   90M     0 100% /snap/core/6130
/dev/loop3                squashfs   18M   18M     0 100% /snap/amazon-ssm-agent/930
/dev/mapper/data-lv--data ext4      1.2T   77M  1.1T   1% /data

创建快照 

现在我们再讲一下快照：

通过使用lvm的快照我们可以轻松的备份数据，由于snapshot和源lvm的关系，snapshot只能够临时使用，不能脱离源lvm而存在.

当一个snapshot创建的时候，仅拷贝原始卷里的数据，这部是物理上的数据拷贝，因此snapshot创建的特别块，当原始卷里的数据由写入时，备份卷开始记录原始卷哪些数据发生了变化，然后在原始卷新书局覆盖旧数据时，将旧数据拷贝到snapshot的预留空间中，起到备份数据的作用，就保证了所有数据和创建备份卷之前的数据一致性。
snapshot的特点：
采用COW实现方式时，snapshot的大小并不需要和原始卷一样大
1、根据原始卷数据的改变大小范围来设置
2、根据原始卷数据的更新频率来定，一旦snapshot的空间记录满了原始卷块变换的信息，那么这个snapshot就不能使用了
lvcreate -L 50M -n lv0backup -s /dev/vg0/lv0
创建一个50M 名字为lv0backup源设备为/dev/vg0/lv0的快照
此快照不需要格式化，直接进行挂载使用就行。

删除快照

1、首先是确定一下之前创建快照的路径

[root@chaofeng mapper]# lvdisplay
  --- Logical volume ---
  LV Path                /dev/data/lv-data
  LV Name                lv-data
  VG Name                data
  LV UUID                DKIkKT-b7yU-9jSZ-I4fk-4Knb-NQHe-9gWgbL
  LV Write Access        read/write
  LV Creation host, time chaofeng, -- :: +
  LV snapshot status     source of
                         data_snap [INACTIVE]
  LV Status              available
  # open
  LV Size                19.50 GiB
  Current LE
  Segments
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to
  Block device           :

  --- Logical volume ---
  LV Path                /dev/data/data_snapp
  LV Name                data_snap
  VG Name                data
  LV UUID                IBJMrz-leJD-EbVs-YyGZ-IUJT-da0k-0FN5Hy
  LV Write Access        read/write
  LV Creation host, time chaofeng, -- :: +
  LV snapshot status     INACTIVE destination for lv-data
  LV Status              available
  # open
  LV Size                19.50 GiB
  Current LE
  COW-table size         4.00 MiB
  COW-table LE
  Snapshot chunk size    4.00 KiB
  Segments
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to
  Block device           :

确定好之后开始删除

[root@chaofeng data]# lvremove  /dev/data/data_snap
Do you really want to remove active logical volume data/data_snap? [y/n]: y
  Logical volume "data_snap" successfully removed

此刻我们已经删除了快照所在的那块分区了。

缩减LVM空间大小

首先查看一下原LVM空间大小

[root@chaofeng data]# lvdisplay
  --- Logical volume ---
  LV Path                /dev/data/lv-data
  LV Name                lv-data
  VG Name                data
  LV UUID                DKIkKT-b7yU-9jSZ-I4fk-4Knb-NQHe-9gWgbL
  LV Write Access        read/write
  LV Creation host, time chaofeng, -- :: +
  LV Status              available
  # open
  LV Size                19.50 GiB
  Current LE
  Segments
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to
  Block device           :

目前LVM空间是19.5G的大小，现在我想缩减到15G。

[root@chaofeng data]# lvreduce -L 15G /dev/data/lv-data
  WARNING: Reducing active logical volume to 15.00 GiB.
  THIS MAY DESTROY YOUR DATA (filesystem etc.)
Do you really want to reduce data/lv-data? [y/n]: y
  Size of logical volume data/lv-data changed from 19.50 GiB ( extents) to 15.00 GiB ( extents).
  Logical volume data/lv-data successfully resized.
[root@chaofeng data]# lvdisplay
  --- Logical volume ---
  LV Path                /dev/data/lv-data
  LV Name                lv-data
  VG Name                data
  LV UUID                DKIkKT-b7yU-9jSZ-I4fk-4Knb-NQHe-9gWgbL
  LV Write Access        read/write
  LV Creation host, time chaofeng, -- :: +
  LV Status              available
  # open
  LV Size                15.00 GiB
  Current LE
  Segments
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to
  Block device           :

此时已经缩减成功了。

在LVM的一些预留空间上创建swap分区

刚刚我们看到把19.5G的空间缩减到15G，也就是说此时lvm还有4.5G左右的空间预留，那我们来把这部分空间划做交换分区来使用

[root@chaofeng data]# lvcreate  --help | head　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　#先查看一下命令创建的语法
  lvcreate - Create a logical volume

  Create a linear LV.
  lvcreate -L|--size Size[m|UNIT] VG
    [ -l|--extents Number[PERCENT] ]
    [    --type linear ]
    [ COMMON_OPTIONS ]
    [ PV ... ]

  Create a striped LV (infers --type striped).

[root@chaofeng data]# vgdisplay　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　#再确定一下VG组的名字
  --- Volume group ---
  VG Name               data
  System ID
  Format                lvm2
  Metadata Areas
  Metadata Sequence No
  VG Access             read/write
  VG Status             resizable
  MAX LV
  Cur LV
  Open LV
  Max PV
  Cur PV
  Act PV
  VG Size               <20.00 GiB
  PE Size               4.00 MiB
  Total PE
  Alloc PE / Size        / 15.00 GiB
  Free  PE / Size        / <5.00 GiB
  VG UUID               46OJtj-IL0F-StLt-aj5H-I5Au-wE7W-rk3l5l
[root@chaofeng data]# lvcreate -L 4G -n swap_lvm data　　　　　　　　　　　　　　　　　　　　　　　　　　#创建
  Logical volume "swap_lvm" created.

此时已经创建成功了。那接下来我们就要进行格式化并挂载了

[root@chaofeng mapper]# mkswap /dev/mapper/data-swap_lvm
正在设置交换空间版本 ，大小 =  KiB
无标签，UUID=5f25be8c-ef13-485b-a243-4f13041ffcc9

　[root@chaofeng mapper]# cat /etc/fstab

#
# /etc/fstab
# Created by anaconda on Fri Jan 4 20:31:39 2019
#
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
/dev/mapper/centos-root / xfs defaults 0 0
UUID=84629116-e18f-4776-9204-aaa79fee0844 /boot xfs defaults 0 0
/dev/mapper/centos-swap swap swap defaults 0 0
/dev/mapper/data-swap_lvm swap swap defaults 0 0　　　　　　　　　　　　　　　　　　　　　　　　　　#要在/etc/fstab里面添加这句话

[root@chaofeng mapper]# swapon -a
[root@chaofeng mapper]# free -h
              total        used        free      shared  buff/cache   available
Mem:           972M        169M        553M        7.6M        249M        603M
Swap:          .7G          0B        .7G

到此我们的swap分区已经添加成功。