内核模块dm可以实现以下功能
快照：保留数据当时状态，提供数据另外访问路径。如果访问快照里面的数据没改变，那么会使用原来路径，如果发生改变则访问快照数据。可以用来进行备份。
多路径：每条路径，操作系统会认为是一个实际存在的物理盘，但实际上只是通向同一个物理盘的不同路径而已
LVM2：
物理卷(PV)：
物理盘区(PE)：逻辑存储单位
逻辑卷组(VG)：为LV提供统一接口容器。镜像功能：在不同物理卷中都存放一份相同数据
逻辑卷(LV)：动态扩展缩减的文件系统
逻辑分区(LE)：指定多个PE为一个LE
快照卷：为逻辑卷预留空间创建快照
LVM操作：
pv:pvcreate,pvremove,pvscan,pvdisplay,pvmove
vg:vgcreate,vgremove,vgextend,vgreduce,vgs,vgscan
lv:lvcreate,lvremove,lvextend,lvreduce,lvresize,lvs,lvdisplay
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[root@localhost ~]# pvcreate /dev/sdd{1,2}
Physical volume "/dev/sdd1" successfully created.
Physical volume "/dev/sdd2" successfully created.
[root@localhost ~]# pvs
PV VG Fmt Attr PSize PFree
/dev/sda2 rhel lvm2 a-- <93.82g 4.00m
/dev/sdd1 lvm2 --- 1.41g 1.41g
/dev/sdd2 lvm2 --- 599.00m 599.00m
详细信息查看pvdisplay
[root@localhost ~]# pvscan
PV /dev/sda2 VG rhel lvm2 [<93.82 GiB / 4.00 MiB free]
PV /dev/sde2 lvm2 [699.00 MiB]
PV /dev/sdf1 lvm2 [600.00 MiB]
PV /dev/sdd2 lvm2 [599.00 MiB]
PV /dev/sdf2 lvm2 [1.41 GiB]
PV /dev/sde1 lvm2 [<1.32 GiB]
PV /dev/sdd1 lvm2 [1.41 GiB]
Total: 7 [99.81 GiB] / in use: 1 [<93.82 GiB] / in no VG: 6 [<6.00 GiB]
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vg操作：
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vgcreate vgname path_to_pv -s指定pe大小默认4M
[root@localhost ~]# vgs -------------------查看vg
VG #PV #LV #SN Attr VSize VFree
rhel 1 2 0 wz--n- <93.82g 4.00m
[root@localhost ~]# vgcreate yellow /dev/sd{d,e,f}{1,2} -------------------创建vg
Volume group "yellow" successfully created
[root@localhost ~]# vgs
VG #PV #LV #SN Attr VSize VFree
rhel 1 2 0 wz--n- <93.82g 4.00m
yellow 6 0 0 wz--n- <5.98g <5.98g
[root@localhost ~]# vgdisplay yellow
--- Volume group ---
VG Name yellow
System ID
Format lvm2
Metadata Areas 6
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 6
Act PV 6
VG Size <5.98 GiB
PE Size 4.00 MiB
Total PE 1530
Alloc PE / Size 0 / 0
Free PE / Size 1530 / <5.98 GiB
VG UUID u5fZZK-BWLN-RtSt-kvL9-cyfr-oJUW-F0e52L
[root@localhost ~]# vgremove yellow --------------删除vg
Volume group "yellow" successfully removed
从vg中删除pv：
[root@localhost ~]# pvs
PV VG Fmt Attr PSize PFree
/dev/sda2 rhel lvm2 a-- <93.82g 4.00m
/dev/sdd1 yellow lvm2 a-- 1.41g 1.41g
/dev/sdd2 yellow lvm2 a-- 596.00m 596.00m
/dev/sde1 yellow lvm2 a-- 1.31g 1.31g
/dev/sde2 yellow lvm2 a-- 696.00m 696.00m
/dev/sdf1 yellow lvm2 a-- 596.00m 596.00m
/dev/sdf2 yellow lvm2 a-- 1.41g 1.41g
[root@localhost ~]# pvmove /dev/sdf2 -----------------先把pv数据移动到其他vg
No data to move for yellow.
[root@localhost ~]# vgreduce yellow /dev/sdf2 -----------------从vg中删除vg
Removed "/dev/sdf2" from volume group "yellow"
[root@localhost ~]# vgs
VG #PV #LV #SN Attr VSize VFree
rhel 1 2 0 wz--n- <93.82g 4.00m
yellow 5 0 0 wz--n- <4.57g <4.57g
[root@localhost ~]# pvs
PV VG Fmt Attr PSize PFree
/dev/sda2 rhel lvm2 a-- <93.82g 4.00m
/dev/sdd1 yellow lvm2 a-- 1.41g 1.41g
/dev/sdd2 yellow lvm2 a-- 596.00m 596.00m
/dev/sde1 yellow lvm2 a-- 1.31g 1.31g
/dev/sde2 yellow lvm2 a-- 696.00m 696.00m
/dev/sdf1 yellow lvm2 a-- 596.00m 596.00m
/dev/sdf2 lvm2 --- 1.41g 1.41g
[root@localhost ~]# pvremove /dev/sdf2 --------------------删除pv
Labels on physical volume "/dev/sdf2" successfully wiped.
[root@localhost ~]# pvs
PV VG Fmt Attr PSize PFree
/dev/sda2 rhel lvm2 a-- <93.82g 4.00m
/dev/sdd1 yellow lvm2 a-- 1.41g 1.41g
/dev/sdd2 yellow lvm2 a-- 596.00m 596.00m
/dev/sde1 yellow lvm2 a-- 1.31g 1.31g
/dev/sde2 yellow lvm2 a-- 696.00m 696.00m
/dev/sdf1 yellow lvm2 a-- 596.00m 596.00m
加入一个vg
[root@localhost ~]# pvcreate /dev/sdf2
Physical volume "/dev/sdf2" successfully created.
[root@localhost ~]# vgextend yellow /dev/sdf2
Volume group "yellow" successfully extended
[root@localhost ~]# vgs
VG #PV #LV #SN Attr VSize VFree
rhel 1 2 0 wz--n- <93.82g 4.00m
yellow 6 0 0 wz--n- <5.98g <5.98g
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lv操作：
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创建lv：
lvcreate -n lv_name -L (大小KMG)[-l 多少个盘区] vg_name
[root@localhost ~]# lvcreate -L 80M -n testlv yellow
Logical volume "testlv" created.
[root@localhost ~]# lvdisplay /dev/yellow/testlv
--- Logical volume ---
LV Path /dev/yellow/testlv
LV Name testlv
VG Name yellow
LV UUID 1zCsL4-YEZt-Nh1P-RTAw-dH7R-LG7B-1cVx5D
LV Write Access read/write
LV Creation host, time localhost.localdomain, 2018-05-30 23:47:15 +0800
LV Status available
# open 0
LV Size 80.00 MiB
Current LE 20
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 8192
Block device 253:2
[root@localhost ~]# mkfs.ext4 -j /dev/yellow/testlv -------------创建文件系统
mke2fs 1.42.9 (28-Dec-2013)
文件系统标签=
OS type: Linux
块大小=1024 (log=0)
分块大小=1024 (log=0)
Stride=0 blocks, Stripe width=0 blocks
20480 inodes, 81920 blocks
4096 blocks (5.00%) reserved for the super user
第一个数据块=1
Maximum filesystem blocks=33685504
10 block groups
8192 blocks per group, 8192 fragments per group
2048 inodes per group
Superblock backups stored on blocks:
8193, 24577, 40961, 57345, 73729
Allocating group tables: 完成
正在写入inode表: 完成
Creating journal (4096 blocks): 完成
Writing superblocks and filesystem accounting information: 完成
[root@localhost ~]# mount /dev/yellow/testlv /mnt/ --------挂在到相关目录
逻辑卷移除：
移除前确认挂载点已经umount
[root@localhost ~]# lvremove /dev/mapper/yellow-testlv
Logical volume yellow/testlv contains a filesystem in use.
[root@localhost ~]# umount /mnt/
[root@localhost ~]# lvremove /dev/mapper/yellow-testlv
Do you really want to remove active logical volume yellow/testlv? [y/n]: y
Logical volume "testlv" successfully removed
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扩展逻辑卷：
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lvextend -L [+]#(加号表示扩展多少，#表示扩展到多少)
[root@localhost mapper]# df -h
文件系统 容量 已用 可用 已用% 挂载点
/dev/mapper/rhel-root 90G 33G 58G 37% /
devtmpfs 1.4G 0 1.4G 0% /dev
tmpfs 1.5G 0 1.5G 0% /dev/shm
tmpfs 1.5G 9.4M 1.4G 1% /run
tmpfs 1.5G 0 1.5G 0% /sys/fs/cgroup
/dev/sda1 1014M 170M 845M 17% /boot
tmpfs 287M 28K 287M 1% /run/user/0
/dev/mapper/yellow-qq 477M 2.3M 445M 1% /uuu
[root@localhost mapper]# vgs ---------------------扩展前查看vg free有足够大小
VG #PV #LV #SN Attr VSize VFree
rhel 1 2 0 wz--n- <93.82g 4.00m
yellow 6 1 0 wz--n- <5.98g <5.49g
[root@localhost mapper]# lvextend -L 2G /dev/yellow/qq
Size of logical volume yellow/qq changed from 500.00 MiB (125 extents) to 2.00 GiB (512 extents).
Logical volume yellow/qq successfully resized.
[root@localhost mapper]# df -h
文件系统 容量 已用 可用 已用% 挂载点
/dev/mapper/rhel-root 90G 33G 58G 37% /
devtmpfs 1.4G 0 1.4G 0% /dev
tmpfs 1.5G 0 1.5G 0% /dev/shm
tmpfs 1.5G 9.4M 1.4G 1% /run
tmpfs 1.5G 0 1.5G 0% /sys/fs/cgroup
/dev/sda1 1014M 170M 845M 17% /boot
tmpfs 287M 28K 287M 1% /run/user/0
/dev/mapper/yellow-qq 477M 2.3M 445M 1% /uuu
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缩减逻辑卷：
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1、不能在线缩减，得先卸载。
2、确保缩减后大小能承载原有数据
3、缩减之前强行检查文件，确保文件系统处于一致性检查
[root@localhost mapper]# umount /uuu
[root@localhost mapper]# e2fsck -f /dev/mapper/yellow-qq
e2fsck 1.42.9 (28-Dec-2013)
第一步: 检查inode,块,和大小
第二步: 检查目录结构
第3步: 检查目录连接性
Pass 4: Checking reference counts
第5步: 检查簇概要信息
/dev/mapper/yellow-qq: 11/128016 files (0.0% non-contiguous), 26684/512000 blocks
[root@localhost mapper]# lvreduce -L 1G /dev/yellow/qq
WARNING: Reducing active logical volume to 1.00 GiB.
THIS MAY DESTROY YOUR DATA (filesystem etc.)
Do you really want to reduce yellow/qq? [y/n]: y
Size of logical volume yellow/qq changed from 2.00 GiB (512 extents) to 1.00 GiB (256 extents).
Logical volume yellow/qq successfully resized.
[root@localhost mapper]# mount /dev/yellow/qq /uuu
[root@localhost mapper]# df -h
文件系统 容量 已用 可用 已用% 挂载点
/dev/mapper/rhel-root 90G 33G 58G 37% /
devtmpfs 1.4G 0 1.4G 0% /dev
tmpfs 1.5G 0 1.5G 0% /dev/shm
tmpfs 1.5G 9.4M 1.4G 1% /run
tmpfs 1.5G 0 1.5G 0% /sys/fs/cgroup
/dev/sda1 1014M 170M 845M 17% /boot
tmpfs 287M 28K 287M 1% /run/user/0
/dev/mapper/yellow-qq 477M 2.3M 445M 1% /uuu
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快照卷：
1、生命周期内数据增长量不能超过快照卷大小（可以指定lv中数据量大小）
2、快照卷是只读的
3、跟原卷在同一个卷组
lvcreate -L(大小) -s(快照卷) -p r|w lv_name
[root@localhost mapper]# lvcreate -L 10M -n testlv_snap -s /dev/yellow/qq -p r
Rounding up size to full physical extent 12.00 MiB
Logical volume "testlv_snap" created.
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镜像卷：
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[root@localhost mapper]# lvcreate -L 1G -m1 -n bbq yellow /dev/sdf1 /dev/sdf2 /dev/sde1
Logical volume "bbq" created.
[root@localhost mapper]# lvs -a -o +devices
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert Devices
root rhel -wi-ao---- 90.00g /dev/sda2(976)
swap rhel -wi-ao---- 3.81g /dev/sda2(0)
bbq yellow rwi-a-r--- 1.00g 100.00 bbq_rimage_0(0),bbq_rimage_1(0)
[bbq_rimage_0] yellow iwi-aor--- 1.00g /dev/sdf2(1)
[bbq_rimage_1] yellow iwi-aor--- 1.00g /dev/sde1(1)
[bbq_rmeta_0] yellow ewi-aor--- 4.00m /dev/sdf2(0)
[bbq_rmeta_1] yellow ewi-aor--- 4.00m /dev/sde1(0)
qq yellow owi-aos--- 1.00g /dev/sdd1(0)
testlv_snap yellow sri-aos--- 12.00m qq 0.10 /dev/sdd1(256)
[root@localhost mapper]# lvdisplay /dev/yellow/bbq
--- Logical volume ---
LV Path /dev/yellow/bbq
LV Name bbq
VG Name yellow
LV UUID mVwhvG-djHj-0jdM-6MlR-T4iG-0vNx-PHz8s4
LV Write Access read/write
LV Creation host, time localhost.localdomain, 2018-05-31 01:25:13 +0800
LV Status available
# open 0
LV Size 1.00 GiB
Current LE 256
Mirrored volumes 2
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 8192
Block device 253:10
[root@localhost ~]# lvextend bbq /dev/sde1
[root@localhost ~]# lvconvert -m1 /dev/yellow/bbq /dev/sde1 /dev/sdf1 /dev/sdf2
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参考：
https://blog.csdn.net/cybertan/article/details/7623356
https://blog.csdn.net/yanggd1987/article/details/48676347