恢复ext4文件系统superblock
1. Create ext4 文件系统。
[root@localhost ~]# mkfs.ext4 /dev/vdb1
[root@localhost ~]# partprobe /dev/vdb

2. 挂载文件系统
[root@localhost ~]# grep vdb2 /etc/fstab
/dev/vdb1    /ext4    ext4    defaults    0 0

[root@localhost ~]# mount -a

[root@localhost ~]# df -h
Filesystem                       Size  Used Avail Use% Mounted on
/dev/vdb1                        100G  1.7G   94G   2% /ext4

3. 卸载文件系统，并破坏super block
[root@localhost ~]# umount /ext4
[root@localhost ~]#  
[root@localhost ~]# dd if=/dev/zero of=/dev/vdb1 bs=1024 count=5
5+0 records in
5+0 records out
5120 bytes (5.1 kB) copied, 0.00481915 s, 1.1 MB/s

[root@localhost ~]# partx /dev/vdb
partx: /dev/vdb: failed to read partition table
[root@localhost ~]#
[root@localhost ~]# mount /ext4
mount: wrong fs type, bad option, bad superblock on /dev/vdb1,
      missing codepage or helper program, or other error
      In some cases useful info is found in syslog - try
      dmesg | tail  or so

[root@localhost ~]# dmesg
[22600278.492089] EXT4-fs (vdb1): VFS: Can't find ext4 filesystem

4. 恢复superblock
[root@localhost ~]# fsck -t ext4 /dev/vdb1
fsck from util-linux 2.20.1
e2fsck 1.41.14 (22-Dec-2010)
fsck.ext4: Superblock invalid, trying backup blocks...
One or more block group descriptor checksums are invalid.  Fix<y>? yes

Group descriptor 0 checksum is invalid.  FIXED.
Group descriptor 1 checksum is invalid.  FIXED.
Group descriptor 2 checksum is invalid.  FIXED.
...
Fix<y>? yes


/dev/vdb1: ***** FILE SYSTEM WAS MODIFIED *****
/dev/vdb1: 11/6553600 files (0.0% non-contiguous), 459349/26214144 blocks

5. 测试是否恢复了。
[root@localhost ~]# mount -a
[root@localhost ~]# df -h
Filesystem                       Size  Used Avail Use% Mounted on
/dev/vdb1                        100G  1.7G   94G   2% /ext4