环境：CentOS 7，分区使用的是默认分区。
一台机器共有4块2T的硬盘，在sda上已经安装有系统，想要扩容。参考网页内容。
仍然存在的问题是，vg扩展到6T以后，vl只能扩展到4T，无法继续扩容，待解决。
结果！！！！居然分次extend就可以继续extend了！！如下所示！！！简直给跪！所以造成这个结果的原因是我这个+后面的数字算错了！！！太弱智了！

[root@localhost ~]# lvextend -L +360558 /dev/centos/home
  Rounding size to boundary between physical extents: 352.11 GiB
  Size of logical volume centos/home changed from 4.03 TiB (1056286 extents) to 4.37 TiB (1146426 extents).
  Logical volume home successfully resized.
[root@localhost ~]# lvextend -L +360558 /dev/centos/home
  Rounding size to boundary between physical extents: 352.11 GiB
  Insufficient free space: 90140 extents needed, but only 90138 available
[root@localhost ~]# lvextend -L +90138 /dev/centos/home 
  Rounding size to boundary between physical extents: 88.03 GiB
  Size of logical volume centos/home changed from 5.06 TiB (1326706 extents) to 5.15 TiB (1349241 extents).
  Logical volume home successfully resized.

1. 查看当前lvm的情况（/dev/sda2）

首先fdisk -l查看当前的分区情况如下所示，sda，sdb，sdc，sdd四块硬盘均已分区，sdbcd各自分为了一个大区，其中sda已有lvm分区/dev/sda2。

[root@localhost ~]# fdisk -l

Disk /dev/sda: 2000.4 GB, 2000398934016 bytes, 3907029168 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: 0x0007dc9b

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048     1026047      512000   83  Linux
/dev/sda2         1026048  3907028991  1953001472   8e  Linux LVM

Disk /dev/sdc: 2000.4 GB, 2000398934016 bytes, 3907029168 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: 0xc3897539

   Device Boot      Start         End      Blocks   Id  System
/dev/sdc1            2048  3907029167  1953513560   83  Linux

Disk /dev/sdd: 2000.4 GB, 2000398934016 bytes, 3907029168 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: 0xc3897517

   Device Boot      Start         End      Blocks   Id  System
/dev/sdd1            2048  3907029167  1953513560   83  Linux

Disk /dev/sdb: 2000.4 GB, 2000398934016 bytes, 3907029168 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: 0xc389752b

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1            2048  3907029167  1953513560   83  Linux

Disk /dev/mapper/centos-root: 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 /dev/mapper/centos-swap: 4294 MB, 4294967296 bytes, 8388608 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 /dev/mapper/centos-home: 1941.8 GB, 1941824339968 bytes, 3792625664 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    

使用命令vgdisplay和lvdisplay查看当前的卷组（Volume group）和逻辑卷（Logical volumes）情况。

[root@localhost ~]# vgdisplay
--- Volume group ---
VG Name               centos
System ID             
Format                lvm2
Metadata Areas        1
Metadata Sequence No  4
VG Access             read/write
VG Status             resizable
MAX LV                0
Cur LV                3
Open LV               3
Max PV                0
Cur PV                1
Act PV                1
VG Size               1.82 TiB
PE Size               4.00 MiB
Total PE              476806
Alloc PE / Size       476791 / 1.82 TiB
Free  PE / Size       15 / 60.00 MiB
VG UUID               o56Jrx-kGgK-bfPO-fROL-5UB1-m21V-K3vi9Z

lv情况如下，分为/dev/centos/swap、/dev/centos/home、 /dev/centos/root三个lv：

[root@localhost ~]# lvdisplay
  --- Logical volume ---
  LV Path                /dev/centos/swap
  LV Name                swap
  VG Name                centos
  LV UUID                H7KpXK-YjfS-ssLE-7gbx-xNnt-QJsQ-hEWcu0
  LV Write Access        read/write
  LV Creation host, time localhost.localdomain, 2016-01-02 20:26:29 +0800
  LV Status              available
  # open                 2
  LV Size                4.00 GiB
  Current LE             1024
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:1
   
  --- Logical volume ---
  LV Path                /dev/centos/home
  LV Name                home
  VG Name                centos
  LV UUID                kveGiy-O6Y2-OMqN-2Ec2-76Ls-TdDh-1Rl3uu
  LV Write Access        read/write
  LV Creation host, time localhost.localdomain, 2016-01-02 20:26:29 +0800
  LV Status              available
  # open                 1
  LV Size                1.77 TiB
  Current LE             462967
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:2
   
  --- Logical volume ---
  LV Path                /dev/centos/root
  LV Name                root
  VG Name                centos
  LV UUID                lOLgfM-Jw1f-zH5e-IOld-kVok-Jr0f-IhNfAK
  LV Write Access        read/write
  LV Creation host, time localhost.localdomain, 2016-01-02 20:27:08 +0800
  LV Status              available
  # open                 1
  LV Size                50.00 GiB
  Current LE             12800
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:0    

2.向当前VG增加一块磁盘sdb的容量

1. 创建一个新的linux lvm格式的分区/dev/sdb1。如果/dev/sdb没有分区，则先分区。而我们的/dev/sdb已经分区为/dev/sdb1一个分区，所以可以直接转换为lvm分区：

   fdisk /dev/sdb
   t #修改分区格式
   8e #指定为LVM分区
   w #写入分区表
   partprobe #重读分区表

2. 给新分区创建PV，加入VG，LV

   pvcreate /dev/sdb1

   加入VG

   vgextend centos /dev/sdb1

   扩展LV

   lvdisplay

   lvextend -L xxxxx /dev/centos/home （增大到xxxxx）

   或者# lvextend -L +xxxx /dev/centos/home （比原来增加xxxx）
   重设LV大小

   resize2fs /dev/centos/home

   如果文件系统为xfs则使用xfs_growfs /dev/centos/home

   df -h