Linux的VPS服务器升级后，硬盘扩容的方法。
比如说df -h看到指令，硬盘为 /dev/xvda1，从100G升级到200G硬盘，只需要执行下面指令。resize2fs /dev/xvda1
貌似，视乎没有反应？发工单给服务器提供商看到SSH貌似执行了
umount -r /dev/xvda1
umount -a /dev/xvda1
fdisk /dev/xvda1
resize2fs /dev/xvda1
这些具体未实测，大致意思就是强制卸载xen的系统盘，然后分区，重载大小，有兴趣可以打个快照试试看。
在使用XEN虚拟化的VPS时，按照向导，在选择存储的时候默认硬盘大小是 8 G，这时候可以根据自己的需要输入一个合适的数字，例如100。完成向导并启动VPS 后登陆机器。使用命令：
df -h
发现硬盘的大小不是自己的设定的值，而还是 8G，使用fdisk来分区和格式化后，还是无法增大其空间。反复折腾多次，包括重启机器，问题依旧，后来发现其实很简单，只需要使用一条命令resize2fs就可以搞定。
resize2fs /dev/xvde
注意：“/dev/xvde” 根据自己的实际情况可能会不一样。使用fdisk或df命令都可以获知具体的设备号。 如果执行上述命令收到 The filesystem is already 2096896 blocks long. Nothing to do! 的错误，那么需要先做如下操作：
<<1>> Look at the filesystem, it is 6G
<<2>> Look at the disk and the partition, the disk is 21.5 GB but the partition is 6 GB (6291456 blocks)
<<3>> Start fdisk for that disk (xvda, so not the partition xvda1)
<<4>> Switch to sector display.
<<5>> Print the partition(s), and remember the start sector (2048 in the example).
<<6>> Delete the partition.
<<7>> Create a new partition.
<<8>> Make it primary.
<<9>> First partition.
<<10>> Enter the old start sector, do NOT make any typo here!!! (2048 in the example)
<<11>> Hit enter to accept the default (this is the remainder of the disk)
<<12>> Print the changes and make sure the start sector is ok, if not restart at <<6>>
<<13>> Make the partition bootable. do NOT forget this!!!
<<14>> Enter your partition number (1 in the example)
<<15>> Write the partition info back, this will end the fdisk session.
<<16>> Reboot the server, and wait for it to come up (this may take longer than usual).
<<17>> Verify the filesystem size.
<<18>> If the filesystem is not around 20Gb as expected, you can use this command.
# df -h<<1>>
Filesystem SizeUsed Avail Use% Mounted on
/dev/xvda1 6.0G2.0G3.7G35% /
tmpfs 15G 0 15G 0% /dev/shm
# fdisk -l<<2>>
Disk /dev/xvda: 21.5 GB, 21474836480 bytes
97 heads, 17 sectors/track, 25435 cylinders
Units = cylinders of 1649 * 512 = 844288 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x0003b587
Device Boot Start End Blocks IdSystem
/dev/xvda1 * 2 7632 6291456 83Linux
# fdisk /dev/xvda<<3>>
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): u<<4>>
Changing display/entry units to sectors
Command (m for help): p<<5>>
Disk /dev/xvda: 21.5 GB, 21474836480 bytes
97 heads, 17 sectors/track, 25435 cylinders, total 41943040 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 identifier: 0x0003b587
Device Boot Start End Blocks IdSystem
/dev/xvda1 * 2048 12584959 6291456 83Linux
Command (m for help): d<<6>>
Selected partition 1
Command (m for help): n<<7>>
Command action
e extended
p primary partition (1-4)
p<<8>>
Partition number (1-4): 1<<9>>
First sector (17-41943039, default 17): 2048<<10>>
Last sector, +sectors or +size{K,M,G} (2048-41943039, default 41943039): <<11>>
Using default value 41943039
Command (m for help): p <<12>>
Disk /dev/xvda: 21.5 GB, 21474836480 bytes
97 heads, 17 sectors/track, 25435 cylinders, total 41943040 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 identifier: 0x0003b587
Device Boot Start End Blocks IdSystem
/dev/xvda1 2048 41943039 20970496 83Linux
Command (m for help): a<<13>>
Partition number (1-4): 1<<14>>
Command (m for help): w<<15>>
The partition table has been altered!
Calling ioctl() to re-read partition table.
WARNING: Re-reading the partition table failed with error 16: ...
The kernel still uses the old table. The new table will be used at
the next reboot or after you run partprobe(8) or kpartx(8)
Syncing disks.
# reboot<<16>>
# df -h<<17>>
Filesystem SizeUsed Avail Use% Mounted on
/dev/xvda1 20G2.0G 17G11% /
tmpfs 15G 0 15G 0% /dev/shm
# resize2fs /dev/xvda1<<18>>
resize2fs 1.41.12 (17-May-2010)
Filesystem at /dev/xvda1 is mounted on /; on-line resizing required
old desc_blocks = 1, new_desc_blocks = 2
Performing an on-line resize of /dev/xvda1 to 5242624 (4k) blocks.
The filesystem on /dev/xvda1 is now 5242624 blocks long.
root@vs120 [~]#df -h
Filesystem SizeUsed Avail Use% Mounted on
/dev/xvda1 20G7.8G 11G42% /
tmpfs 498M 0498M 0% /dev/shm
/usr/tmpDSK 399M 11M368M 3% /tmp
参考互联网：https://serverfault.com/questions/414983/ec2-drive-not-ebs-volume-size
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