又作大死了，求助重新恢复硬盘

OS: Ubuntu 16.04

我打算备份系统到我的硬盘里，也是第一次。然后选择了 dd, 然后看到一条命令:

$ sudo  dd if=/dev/sda of=/dev/sdb

sdb 就是我的硬盘啊，然后我作死地想，如果我直接 dd 到 /dev/sdb 会怎么样呢。然后我就直接试了。。。。

我有点担心，就 ls 了一下当前目录也就是我的硬盘的根目录，悲催的事情发生了，空了！！！！赶紧 cancel 掉。然后发现硬盘没有被挂载了。。。。

重启一下看有没有奇迹，什么也没发生。

$ sudo fdisk -l

Disk /dev/sda: 465.8 GiB, 500107862016 bytes, 976773168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: dos
Disk identifier: 0x0004cba2

Device     Boot     Start       End   Sectors   Size Id Type
/dev/sda1  *         4096 104857599 104853504    50G  7 HPFS/NTFS/exFAT
/dev/sda2       104861694 976771071 871909378 415.8G  f W95 Ext'd (LBA)
/dev/sda5       104861696 396363775 291502080   139G  7 HPFS/NTFS/exFAT
/dev/sda6       687867904 699584511  11716608   5.6G 82 Linux swap / Solari
/dev/sda7       699586560 700364799    778240   380M 83 Linux
/dev/sda8       700366848 798021144  97654297  46.6G 83 Linux
/dev/sda9       798023680 976771071 178747392  85.2G 83 Linux

Partition 2 does not start on physical sector boundary.




Ignoring extra data in partition table 5.
Ignoring extra data in partition table 5.
Ignoring extra data in partition table 5.
Invalid flag 0x0eeb of EBR (for partition 5) will be corrected by w(rite).
Disk /dev/sdb: 1.4 TiB, 1500267937792 bytes, 2930210816 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
Disklabel type: dos
Disk identifier: 0x0004cba2

Device     Boot     Start        End    Sectors   Size Id Type
/dev/sdb1  *         4096  104857599  104853504    50G  7 HPFS/NTFS/exFAT
/dev/sdb2       104861694  976771071  871909378 415.8G  f W95 Ext'd (LBA)
/dev/sdb5       770403513 3291724251 2521320739   1.2T f4 SpeedStor

貌似我的数据还在。

然后试着手动挂载 sdb, sdb1, sdb2, sdb5。报错

$ sudo mount /dev/sdb test

mount: wrong fs type, bad option, bad superblock on /dev/sdb1,
       missing codepage or helper program, or other error

       In some cases useful info is found in syslog - try
       dmesg | tail or so.

在装了” nfs-common “之后 sdb 挂载成功了，然而里面是空的。

求助怎么处理？