linux扩容：分区扩容前先用fdisk把该分区的system id改成lvm（8e）
创建逻辑卷：
创建PV(转换物理卷）--->创建VG--->创建LV，并格式化
fdisk /dev/sdb，创建分区并将id改为8e
fdisk /dev/sdc创建分区并将id改为8e
fdisk /dev/sdd创建分区并将id改为8e
pvscan查看当前是否有物理卷
pvdisplay
1、[root@localhost ~]# pvcreate /dev/sdb1
Physical volume "/dev/sdb1" successfully created.
[root@localhost ~]# pvcreate /dev/sdc1
Physical volume "/dev/sdc1" successfully created.
[root@localhost ~]# pvcreate /dev/sdc1
Physical volume "/dev/sdc1" successfully created.
[root@localhost ~]#
2、创建卷组VG
vgscan、vgdisplay
[root@localhost ~]# vgscan
Reading volume groups from cache.
[root@localhost ~]# vgcreate mail_store /dev/sdc1 /dev/sdb1 /dev/sdd1
Volume group "mail_store" successfully created
[root@localhost ~]#
3、创建LV
[root@localhost ~]# lvscan
[root@localhost ~]# lvdisplay
[root@localhost ~]#
[root@localhost ~]# lvcreate -L 15G（大小） -n mail（名称） mail_store（卷组）
Logical volume "mail" created.
[root@localhost ~]# lvscan
ACTIVE '/dev/mail_store/mail' [15.00 GiB] inherit
[root@localhost ~]# lvdisplay
--- Logical volume ---
LV Path /dev/mail_store/mail
LV Name mail
VG Name mail_store
LV UUID j5Hvhi-ppem-Okz1-CV0o-SnKY-Gkdk-lr2zXU
LV Write Access read/write
LV Creation host, time localhost.localdomain, 2019-12-01 03:11:40 +0800
LV Status available

open 0

LV Size 15.00 GiB
Current LE 3840
Segments 2
Allocation inherit
Read ahead sectors auto

• currently set to 8192
  Block device 253:0

格式化lv为ext4文件类型：mkfs -t ext4 /dev/mail_store/mail
[root@localhost ~]# mkfs -t ext4 /dev/mail_store/mail
mke2fs 1.42.9 (28-Dec-2013)
文件系统标签=
OS type: Linux
块大小=4096 (log=2)
分块大小=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
983040 inodes, 3932160 blocks
196608 blocks (5.00%) reserved for the super user
第一个数据块=0
Maximum filesystem blocks=2151677952
120 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

Allocating group tables: 完成
正在写入inode表: 完成
Creating journal (32768 blocks): 完成
Writing superblocks and filesystem accounting information: 完成
挂载lv到/mnt目录：mount /dev/mail_store/mail /mnt/
[root@localhost ~]# mount /dev/mail_store/mail /mnt/
[root@localhost ~]# df -Th
文件系统 类型 容量 已用 可用 已用% 挂载点
/dev/sda2 ext4 17G 3.5G 13G 22% /
devtmpfs devtmpfs 897M 0 897M 0% /dev
tmpfs tmpfs 912M 0 912M 0% /dev/shm
tmpfs tmpfs 912M 9.1M 903M 1% /run
tmpfs tmpfs 912M 0 912M 0% /sys/fs/cgroup
/dev/sda1 xfs 1014M 175M 840M 18% /boot
tmpfs tmpfs 183M 20K 183M 1% /run/user/1000
/dev/sr0 iso9660 3.8G 3.8G 0 100% /run/media/mcq/RHEL-7.4 Server.x86_64
tmpfs tmpfs 183M 0 183M 0% /run/user/0
/dev/mapper/mail_store-mail ext4 15G 41M 14G 1% /mnt
[root@localhost ~]#

总结步骤：
a、pvcreate /dev/sdc1创建一个新的pv分区
注：可能报错，需要更新分区表，执行partprobe,再执行
partprobe
[root@localhost ~]# pvcreate /dev/sdb2
Physical volume "/dev/sdb2" successfully created.

b、vgextand ROOT /dev/sdc1将新的pv分区扩容到vg组ROOT
[root@localhost ~]# vgextend VAR /dev/sdb2
Volume group "VAR" successfully extended

c、lvextend /dev/VAR/var /dev/sdb2或 lvextend -L +20G /dev/VAR/var 将新扩容的空间放入lv卷
[root@localhost ~]# lvextend /dev/VAR/var /dev/sdb2
Size of logical volume VAR/var changed from 2.00 GiB (512 extents) to <12.00 GiB (3071 extents).
Logical volume VAR/var successfully resized.

d、resize2fs /dev/VAR/var
[root@localhost ~]# resize2fs /dev/VAR/var
resize2fs 1.42.9 (28-Dec-2013)
Filesystem at /dev/VAR/var is mounted on /var; on-line resizing required
old_desc_blocks = 1, new_desc_blocks = 2
The filesystem on /dev/VAR/var is now 3144704 blocks long.

df -Th能看到/dev/VAR/var已经扩容