I got these error message from dmesg, it's from a 500 GB SATA disk:

ata2: translated ATA stat/err 0x51/40 to SCSI SK/ASC/ASCQ 0x3/11/04
ata2: status=0x51 { DriveReady SeekComplete Error }
ata2: error=0x40 { UncorrectableError }
ata2: translated ATA stat/err 0x51/40 to SCSI SK/ASC/ASCQ 0x3/11/04
ata2: status=0x51 { DriveReady SeekComplete Error }
ata2: error=0x40 { UncorrectableError }
ata2: translated ATA stat/err 0x51/40 to SCSI SK/ASC/ASCQ 0x3/11/04
ata2: status=0x51 { DriveReady SeekComplete Error }
ata2: error=0x40 { UncorrectableError }
ata2: translated ATA stat/err 0x51/40 to SCSI SK/ASC/ASCQ 0x3/11/04
ata2: status=0x51 { DriveReady SeekComplete Error }
ata2: error=0x40 { UncorrectableError }
ata2: translated ATA stat/err 0x51/40 to SCSI SK/ASC/ASCQ 0x3/11/04
ata2: status=0x51 { DriveReady SeekComplete Error }
ata2: error=0x40 { UncorrectableError }
ata2: translated ATA stat/err 0x51/40 to SCSI SK/ASC/ASCQ 0x3/11/04
ata2: status=0x51 { DriveReady SeekComplete Error }
ata2: error=0x40 { UncorrectableError }
scsi1: ERROR on channel 0, id 0, lun 0, CDB: Read (10) 00 27 c4 00 28 00 00 08 00
Current sdb: sense key Medium Error
Additional sense: Unrecovered read error - auto reallocate failed
end_request: I/O error, dev sdb, sector 667156520
ata2: translated ATA stat/err 0x51/40 to SCSI SK/ASC/ASCQ 0x3/11/04
ata2: status=0x51 { DriveReady SeekComplete Error }
ata2: error=0x40 { UncorrectableError }
scsi1: ERROR on channel 0, id 0, lun 0, CDB: Read (10) 00 27 c4 00 29 00 00 07 00
Current sdb: sense key Medium Error
Additional sense: Unrecovered read error - auto reallocate failed
end_request: I/O error, dev sdb, sector 667156521
ata2: translated ATA stat/err 0x51/40 to SCSI SK/ASC/ASCQ 0x3/11/04
ata2: status=0x51 { DriveReady SeekComplete Error }
ata2: error=0x40 { UncorrectableError }
scsi1: ERROR on channel 0, id 0, lun 0, CDB: Read (10) 00 27 c4 00 2a 00 00 06 00
Current sdb: sense key Medium Error
Additional sense: Unrecovered read error - auto reallocate failed
end_request: I/O error, dev sdb, sector 667156522
ata2: translated ATA stat/err 0x51/40 to SCSI SK/ASC/ASCQ 0x3/11/04
ata2: status=0x51 { DriveReady SeekComplete Error }
ata2: error=0x40 { UncorrectableError }
scsi1: ERROR on channel 0, id 0, lun 0, CDB: Read (10) 00 27 c4 00 2b 00 00 05 00
Current sdb: sense key Medium Error
Additional sense: Unrecovered read error - auto reallocate failed
end_request: I/O error, dev sdb, sector 667156523
ata2: translated ATA stat/err 0x51/40 to SCSI SK/ASC/ASCQ 0x3/11/04
ata2: status=0x51 { DriveReady SeekComplete Error }
ata2: error=0x40 { UncorrectableError }
scsi1: ERROR on channel 0, id 0, lun 0, CDB: Read (10) 00 27 c4 00 2c 00 00 04 00
Current sdb: sense key Medium Error
Additional sense: Unrecovered read error - auto reallocate failed
end_request: I/O error, dev sdb, sector 667156524
ata2: translated ATA stat/err 0x51/40 to SCSI SK/ASC/ASCQ 0x3/11/04
ata2: status=0x51 { DriveReady SeekComplete Error }
ata2: error=0x40 { UncorrectableError }
scsi1: ERROR on channel 0, id 0, lun 0, CDB: Read (10) 00 27 c4 00 2d 00 00 03 00
Current sdb: sense key Medium Error
Additional sense: Unrecovered read error - auto reallocate failed
end_request: I/O error, dev sdb, sector 667156525
ata2: translated ATA stat/err 0x51/40 to SCSI SK/ASC/ASCQ 0x3/11/04
ata2: status=0x51 { DriveReady SeekComplete Error }
ata2: error=0x40 { UncorrectableError }
scsi1: ERROR on channel 0, id 0, lun 0, CDB: Read (10) 00 27 c4 00 2e 00 00 02 00
Current sdb: sense key Medium Error
Additional sense: Unrecovered read error - auto reallocate failed
end_request: I/O error, dev sdb, sector 667156526
EXT3-fs error (device sdb1): read_inode_bitmap: Cannot read inode bitmap - block_group = 2545, inode_bitmap = 83394561
Aborting journal on device sdb1.
EXT3-fs error (device sdb1) in ext3_new_inode: IO failure
EXT3-fs error (device sdb1) in ext3_mkdir: IO failure

Solution:
As suggested here SATA Disk Problems with suggested solutions | Planet Admon , it's suggested to replace the harddisk.