[CentOS] Problems reading a backup data DVD

I wrote a bunch of files to a backup DVD about two months ago and now
neither of my drives will read it.  I get mount errors from "not a
directory" to something like "unrecognized file system type" and so on,
usually after a really long wait and a notice about how the drive is
write-protected (duh).

Here's what happened most recently:

# mount /dev/hdc /mnt
mount: block device /dev/hdc is write-protected, mounting read-only
mount: wrong fs type, bad option, bad superblock on /dev/hdc,
       missing codepage or other error
       In some cases useful info is found in syslog - try
       dmesg | tail  or so
# dmesg | tail -40
hdc: cdrom_decode_status: status=0x51 { DriveReady SeekComplete Error }
hdc: cdrom_decode_status: error=0x40 { LastFailedSense=0x04 }
ide: failed opcode was: unknown
hdc: cdrom_decode_status: status=0x51 { DriveReady SeekComplete Error }
hdc: cdrom_decode_status: error=0x40 { LastFailedSense=0x04 }
ide: failed opcode was: unknown
hdc: cdrom_decode_status: status=0x51 { DriveReady SeekComplete Error }
hdc: cdrom_decode_status: error=0x40 { LastFailedSense=0x04 }
ide: failed opcode was: unknown
hdc: ide_intr: huh? expected NULL handler on exit
hdc: ATAPI reset complete
end_request: I/O error, dev hdc, sector 5118720
Buffer I/O error on device hdc, logical block 639840
hdc: cdrom_decode_status: status=0x51 { DriveReady SeekComplete Error }
hdc: cdrom_decode_status: error=0x40 { LastFailedSense=0x04 }
ide: failed opcode was: unknown
hdc: cdrom_decode_status: status=0x51 { DriveReady SeekComplete Error }
hdc: cdrom_decode_status: error=0x40 { LastFailedSense=0x04 }
ide: failed opcode was: unknown
hdc: cdrom_decode_status: status=0x51 { DriveReady SeekComplete Error }
hdc: cdrom_decode_status: error=0x40 { LastFailedSense=0x04 }
ide: failed opcode was: unknown
hdc: cdrom_decode_status: status=0x51 { DriveReady SeekComplete Error }
hdc: cdrom_decode_status: error=0x40 { LastFailedSense=0x04 }
ide: failed opcode was: unknown
hdc: ide_intr: huh? expected NULL handler on exit
hdc: ATAPI reset complete
hdc: cdrom_decode_status: status=0x51 { DriveReady SeekComplete Error }
hdc: cdrom_decode_status: error=0x40 { LastFailedSense=0x04 }
ide: failed opcode was: unknown
hdc: cdrom_decode_status: status=0x51 { DriveReady SeekComplete Error }
hdc: cdrom_decode_status: error=0x40 { LastFailedSense=0x04 }
ide: failed opcode was: unknown
hdc: cdrom_decode_status: status=0x51 { DriveReady SeekComplete Error }
hdc: cdrom_decode_status: error=0x40 { LastFailedSense=0x04 }
ide: failed opcode was: unknown
hdc: ide_intr: huh? expected NULL handler on exit
hdc: ATAPI reset complete
end_request: I/O error, dev hdc, sector 64
isofs_fill_super: bread failed, dev=hdc, iso_blknum=16, block=16

Is there any way to read what's on this DVD (so I can back -up the files
again, hopefully with better results)?

Secondary related question:  I noticed that my CentOS boot DVD does not
automount when I put it in either drive - why is that?

Thanks.

mhr
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