Cannot mount disks after installing Fedora 15

Question

In short, this is where I found the best answers to my problem with my disks: https://help.ubuntu.com/community/DataRecovery

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During Fedora 15 installation, I added all my 3 drives to be mounted on boot. However, after the installation ended I could not mount them any more. So I came back to Fedora 14 in the hope it was a bug, but, it was not.

I added them in fstab:

$ nano /etc/fstab
/dev/sdb                /media/Unus                     ext4     defaults   0 0
/dev/sdc                /media/Duo                     ext4     defaults       0 0

But they do not mount:

$ mount media/Duo
mount: wrong fs type, bad option, bad superblock on /dev/sdb,
       missing codepage or helper program, or other error
       In some cases useful info is found in syslog - try
       dmesg | tail  or so

This is what I get from dmesg:

$ dmesg | tail
[  897.592207] EXT4-fs (sdc): VFS: Can't find ext4 filesystem

However, the disks are there:

$ testDisk

Disk /dev/sdb - 1000 GB / 931 GiB - ATA ST31000528AS
Disk /dev/sdc - 2000 GB / 1863 GiB - ATA ST2000DL003-9VT1

Disk /dev/sdb - 1000 GB / 931 GiB - CHS 121601 255 63
    Partition                  Start        End    Size in sectors
>   P ext4                     0   0  1 121601  80 63 1953525168 [Unus]

Disk /dev/sdc - 2000 GB / 1863 GiB - CHS 243201 255 63
    Partition                  Start        End    Size in sectors
>   P Unknown                  0   0  1 243201  80 63 3907029168

Note that just before installing Fedora 15, both disks were formated with ext4 and were working normally.

Is there a way to rebuild the filesystem without loosing the data reccorded on the disks?

I wish to know what I should do for both disks have andispensable data in them.

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UPDATE

Some screenshots of the disks:

# fdisk -l

Disk /dev/sdc: 2000.4 GB, 2000398934016 bytes
255 heads, 63 sectors/track, 243201 cylinders, total 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 identifier: 0x34cd78a8

   Device Boot      Start         End      Blocks   Id  System
/dev/sdc1            2048  3907028991  1953513472   8e  Linux LVM

Answer 1

You're trying to mount the whole disk when you should be mounting the partition that contains the the filesystem. So instead of /dev/sdb and /dev/sdc you should be mounting /dev/sdb1 and /dev/sdc1.

So if you change your /etc/fstab to look like this then it should work:

/dev/sdb1  /media/Unus  ext4  defaults  0 0
/dev/sdc1  /media/Duo   ext4  defaults  0 0

In addition, it now appears that these partitions are actually physical volumes (PVs) which presumably contain logical volumes. Most likely linux has already recognised that and started the logical volumes, in which case you should find devices in the /dev/mapper directory that correspond to the logical volumes and you want to specify those devices in /etc/fstab instead of the disk partitions.