[root@lala]# fsck -v -y /dev/sdb1 
fsck 1.37 (21-Mar-2005)
e2fsck 1.37 (21-Mar-2005)
Group descriptors look bad... trying backup blocks...
fsck.ext3: Bad magic number in super-block while trying to open /dev/sdb1

The superblock could not be read or does not describe a correct ext2
filesystem.  If the device is valid and it really contains an ext2
filesystem (and not swap or ufs or something else), then the superblock
is corrupt, and you might try running e2fsck with an alternate superblock:
    e2fsck -b 8193 <device>

[root@backup backups]# e2fsck -b 8193 /dev/sdb1 
e2fsck 1.37 (21-Mar-2005)
e2fsck: Bad magic number in super-block while trying to open /dev/sdb1

[root@lala]# dmesg | tail
EXT3-fs error (device sdb1): ext3_check_descriptors: Block bitmap for group 2960 not in group (block 67108864)!
EXT3-fs: group descriptors corrupted !