硬盘快满了，加硬盘扩容，不管是独立的服务器，还是云空间新买的硬盘，扩容方式一样。下面以阿里VPS为例，详细说一下，挂载硬盘扩容的2种方法。
阿里VPS，个人觉得有以下二个方面需要改进
1，默认不是lvm，所以系统盘/dev/xvda1是不能扩容的，所以如果有大数据的东西，一开始就要考虑到扩容的问题。数据量越大，操作风险越大。
2，不能实现无缝扩容，也就是说，在后台扩容一下，不用登录到VPS，进行调整。非专业人士，扩容困难

一，不采用lvm，直接将硬盘挂载到目录
1，查看硬盘分区情况

复制代码代码如下:
[root@iZ94zz3wqciZ ~]# df
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/xvda1 20641404 14778400 4814480 76% /
tmpfs 509300 0 509300 0% /dev/shm

[root@iZ94zz3wqciZ ~]# fdisk -l

Disk /dev/xvda: 21.5 GB, 21474836480 bytes
255 heads, 63 sectors/track, 2610 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00078f9c

Device Boot Start End Blocks Id System
/dev/xvda1 * 1 2611 20970496 83 Linux //id是83，非lvm

Disk /dev/xvdb: 23.6 GB, 23622320128 bytes //新买的硬盘
255 heads, 56 sectors/track, 3230 cylinders
Units = cylinders of 14280 * 512 = 7311360 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x27cc1f5a

2，硬盘分区并查看分区情况

复制代码代码如下:
[root@iZ94zz3wqciZ ~]# fdisk -S 56 /dev/xvdb //分区

WARNING: DOS-compatible mode is deprecated. It's strongly recommended to
switch off the mode (command 'c') and change display units to
sectors (command 'u').

Command (m for help): n //输入n
Command action
e extended
p primary partition (1-4)
p //主分区
Partition number (1-4): 1 //分区号1
First cylinder (1-3230, default 1):
Using default value 1
Last cylinder, +cylinders or +size{K,M,G} (1-3230, default 3230):
Using default value 3230

Command (m for help): wq //保存并退出
The partition table has been altered!

[root@iZ94zz3wqciZ ~]# fdisk -l

Disk /dev/xvda: 21.5 GB, 21474836480 bytes
255 heads, 63 sectors/track, 2610 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00078f9c

Device Boot Start End Blocks Id System
/dev/xvda1 * 1 2611 20970496 83 Linux

Disk /dev/xvdb: 23.6 GB, 23622320128 bytes
255 heads, 56 sectors/track, 3230 cylinders
Units = cylinders of 14280 * 512 = 7311360 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x27cc1f5a

Device Boot Start End Blocks Id System
/dev/xvdb1 1 3230 23062172 83 Linux //分区后

3，格式化新分区xvdb1

复制代码代码如下:
[root@iZ94zz3wqciZ ~]# mkfs.ext4 /dev/xvdb1 //格式化分区
mke2fs 1.41.12 (17-May-2010)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
1441792 inodes, 5765543 blocks
288277 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=4294967296
176 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

Writing inode tables: done
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 35 mounts or
180 days, whichever comes first. Use tune2fs -c or -i to override.

4，创建目录，并挂载分区

复制代码代码如下:
[root@iZ94zz3wqciZ ~]# mkdir /mnt/fastdfs //挂载目录
[root@iZ94zz3wqciZ ~]# echo "/dev/xvdb1 /mnt/fastdfs ext4 defaults 0 0" /etc/fstab //重启会自动挂载
[root@iZ94zz3wqciZ ~]# mount -a //挂载所有目录

[root@iZ94zz3wqciZ ~]# df
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/xvda1 20641404 14778404 4814476 76% /
tmpfs 509300 0 509300 0% /dev/shm
/dev/xvdb1 22694396 176064 21365516 1% /mnt/fastdfs //新的分区已挂载

到这儿，就把一块独立的硬盘加到系统当中了。这种扩容的方式操作简单，但是扩展性不强，不推荐这种扩容方式。

二，采用lvm的方式，进行硬盘扩容（推荐）
1，取消前面测试的挂载，并删除分区

复制代码代码如下:
[root@iZ94zz3wqciZ ~]# umount -a //取消挂载

[root@iZ94zz3wqciZ ~]# fdisk /dev/xvdb //分区

WARNING: DOS-compatible mode is deprecated. It's strongly recommended to
switch off the mode (command 'c') and change display units to
sectors (command 'u').

Command (m for help): d //删除分区
Selected partition 1

Command (m for help): wq //保存
The partition table has been altered!

2，安装lvm

复制代码代码如下:
[root@iZ94zz3wqciZ nginx]# uname -a //查看内核信息
Linux iZ94zz3wqciZ 2.6.32-431.23.3.el6.x86_64 #1 SMP Thu Jul 31 17:20:51 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux

[root@iZ94zz3wqciZ ~]# yum install lvm2 device-mapper //安装 LVM2，2.6.9以后版本不用装device-mapper

[root@iZ94zz3wqciZ nginx]# lsmod | grep dm_mod //是否加载了dm_mod
dm_mod 84337 5 dm_mirror,dm_log

lvm的安装,首先加载device-mapper模块，从linux内核2.6.9开始，device-mapper模块就已经包含在内，所以你只需加载即可。加载mapper模块：modprobe dm_mod。
3，创建lvm分区

复制代码代码如下:
[root@iZ94zz3wqciZ ~]# fdisk /dev/xvdb //分区

WARNING: DOS-compatible mode is deprecated. It's strongly recommended to
switch off the mode (command 'c') and change display units to
sectors (command 'u').

Command (m for help): l

0 Empty 24 NEC DOS 81 Minix / old Lin bf Solaris
1 FAT12 39 Plan 9 82 Linux swap / So c1 DRDOS/sec (FAT-
2 XENIX root 3c PartitionMagic 83 Linux c4 DRDOS/sec (FAT-
3 XENIX usr 40 Venix 80286 84 OS/2 hidden C: c6 DRDOS/sec (FAT-
4 FAT16 <32M 41 PPC PReP Boot 85 Linux extended c7 Syrinx
5 Extended 42 SFS 86 NTFS volume set da Non-FS data
6 FAT16 4d QNX4.x 87 NTFS volume set db CP/M / CTOS / .
7 HPFS/NTFS 4e QNX4.x 2nd part 88 Linux plaintext de Dell Utility
8 AIX 4f QNX4.x 3rd part 8e Linux LVM df BootIt
9 AIX bootable 50 OnTrack DM 93 Amoeba e1 DOS access
a OS/2 Boot Manag 51 OnTrack DM6 Aux 94 Amoeba BBT e3 DOS R/O
b W95 FAT32 52 CP/M 9f BSD/OS e4 SpeedStor
c W95 FAT32 (LBA) 53 OnTrack DM6 Aux a0 IBM Thinkpad hi eb BeOS fs
e W95 FAT16 (LBA) 54 OnTrackDM6 a5 FreeBSD ee GPT
f W95 Ext'd (LBA) 55 EZ-Drive a6 OpenBSD ef EFI (FAT-12/16/
10 OPUS 56 Golden Bow a7 NeXTSTEP f0 Linux/PA-RISC b
11 Hidden FAT12 5c Priam Edisk a8 Darwin UFS f1 SpeedStor
12 Compaq diagnost 61 SpeedStor a9 NetBSD f4 SpeedStor
14 Hidden FAT16 <3 63 GNU HURD or Sys ab Darwin boot f2 DOS secondary
16 Hidden FAT16 64 Novell Netware af HFS / HFS+ fb VMware VMFS
17 Hidden HPFS/NTF 65 Novell Netware b7 BSDI fs fc VMware VMKCORE
18 AST SmartSleep 70 DiskSecure Mult b8 BSDI swap fd Linux raid auto
1b Hidden W95 FAT3 75 PC/IX bb Boot Wizard hid fe LANstep
1c Hidden W95 FAT3 80 Old Minix be Solaris boot ff BBT
1e Hidden W95 FAT1

Command (m for help): n
Command action
e extended
p primary partition (1-4)
p
Partition number (1-4): 1
First cylinder (1-2871, default 1):
Using default value 1
Last cylinder, +cylinders or +size{K,M,G} (1-2871, default 2871):
Using default value 2871

Command (m for help): p

Disk /dev/xvdb: 23.6 GB, 23622320128 bytes
255 heads, 63 sectors/track, 2871 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x27cc1f5a

Device Boot Start End Blocks Id System
/dev/xvdb1 1 2871 23061276 83 Linux //不是lvm分区格式

Command (m for help): t //转换
Selected partition 1
Hex code (type L to list codes): 8e //换成8e
Changed system type of partition 1 to 8e (Linux LVM)

Command (m for help): p

Disk /dev/xvdb: 23.6 GB, 23622320128 bytes
255 heads, 63 sectors/track, 2871 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x27cc1f5a

Device Boot Start End Blocks Id System
/dev/xvdb1 1 2871 23061276 8e Linux LVM //现在lvm分区格式了

Command (m for help): wq
The partition table has been altered!

Calling ioctl() to re-read partition table.
Syncing disks.

4，创建逻辑卷组，以及逻辑卷等

复制代码代码如下:
[root@iZ94zz3wqciZ ~]# pvcreate /dev/xvdb1 //创建物理卷
Physical volume "/dev/xvdb1" successfully created

[root@iZ94zz3wqciZ ~]# vgcreate myfiles /dev/xvdb1 //创建逻辑卷组
Volume group "myfiles" successfully created

[root@iZ94zz3wqciZ ~]# vgchange -ay myfiles //激活逻辑卷组
0 logical volume(s) in volume group "myfiles" now active

[root@iZ94zz3wqciZ ~]# vgdisplay myfiles | grep "Total PE" //查看该卷组所有的PE
Total PE 5629

[root@iZ94zz3wqciZ ~]# lvcreate -l 5629 -n fastdfs myfiles //创建逻辑卷
Logical volume "fastdfs" created.
 
5，格式化逻辑卷

复制代码代码如下:
[root@iZ94zz3wqciZ ~]# mkfs.ext4 /dev/myfiles/fastdfs //格式化逻辑卷
mke2fs 1.41.12 (17-May-2010)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
1441792 inodes, 5764096 blocks
288204 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=4294967296
176 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

Writing inode tables: done
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 39 mounts or
180 days, whichever comes first. Use tune2fs -c or -i to override.

6,设置自动挂载，并查看分区

复制代码代码如下:
[root@iZ94zz3wqciZ ~]# echo '/dev/myfiles/fastdfs /mnt/fastdfs ext4 defaults 0 0' /etc/fstab //自动挂载
[root@iZ94zz3wqciZ ~]# mount -a //手动挂载
[root@iZ94zz3wqciZ ~]# df
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/xvda1 20641404 14778608 4814272 76% /
tmpfs 509300 0 509300 0% /dev/shm
/dev/mapper/myfiles-fastdfs
22694396 176064 21365516 1% /mnt/fastdfs //lvm逻辑卷已挂载

[root@iZ94zz3wqciZ ~]# reboot //操作完最好重启一下

7，再扩容一块硬盘到已有逻辑卷

复制代码代码如下:
[root@iZ94zz3wqciZ ~]# fdisk /dev/xvdc //详细过程同上，就不详细说明了

[root@iZ94zz3wqciZ ~]# reboot

[root@iZ94zz3wqciZ ~]# pvcreate /dev/xvdc1 //创建物理卷
Physical volume "/dev/xvdc1" successfully created

[root@iZ94zz3wqciZ ~]# vgextend myfiles /dev/xvdc1 //将新硬盘加入卷组
Volume group "myfiles" successfully extended

[root@iZ94zz3wqciZ ~]# vgdisplay myfiles | grep "Total PE" //查看所有PE
Total PE 6907

[root@iZ94zz3wqciZ ~]# lvresize -l 6907 /dev/myfiles/fastdfs //重新规定大小
Size of logical volume myfiles/fastdfs changed from 21.99 GiB (5629 extents) to 26.98 GiB (6907 extents).
Logical volume fastdfs successfully resized

[root@iZ94zz3wqciZ ~]# resize2fs /dev/myfiles/fastdfs //重新规定大小
resize2fs 1.41.12 (17-May-2010)
Filesystem at /dev/myfiles/fastdfs is mounted on /mnt/fastdfs; on-line resizing required
old desc_blocks = 2, new_desc_blocks = 2
Performing an on-line resize of /dev/myfiles/fastdfs to 7072768 (4k) blocks.
The filesystem on /dev/myfiles/fastdfs is now 7072768 blocks long.

[root@iZ94zz3wqciZ ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/xvda1 20G 15G 4.6G 76% /
tmpfs 498M 0 498M 0% /dev/shm
/dev/mapper/myfiles-fastdfs
27G 172M 26G 1% /mnt/fastdfs //新的5G硬盘加上去了

如果是频繁的扩容硬盘的话，LVM是首选，扩展真的很方便。