в този случая cd-rom е външен и работи с usb

dd if=/dev/sr0  of=/dev/null
1100884+0 records in
1100884+0 records out
563652608 bytes (564 MB) copied, 117.119 s, 4.8 MB/s

в случая в cd-romа имаме поставен диск с FreeBSD-9.0-RELEASE-amd64-bootonly.iso

dd if=/dev/sr0 | md5sum –  /home/user/Downloads/FreeBSD-9.0-RELEASE-amd64-bootonly.iso
dd: reading `/dev/sr0′: Input/output error
1253496+0 records in
1253496+0 records out
641789952 bytes (642 MB) copied, 152.657 s, 4.2 MB/s
1598f67a9b15a8618e7eebe959fd3fbf –
477019a305797186a8b3e4147f44edec FreeBSD-9.0-RELEASE-amd64-bootonly.iso

най-вероятно USB към IDE контролера бъгва

706.039473] sr 8:0:0:0: [sr0] Add. Sense: Illegal mode for this track
[ 706.039484] sr 8:0:0:0: [sr0] CDB: Read(10): 28 00 00 04 c8 1e 00 00 01 00
[ 706.039503] end_request: I/O error, dev sr0, sector 1253496
[ 706.039512] Buffer I/O error on device sr0, logical block 313374
[ 706.543311] sr 8:0:0:0: [sr0] Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE
[ 706.543325] sr 8:0:0:0: [sr0] Sense Key : Illegal Request [current]

друга много полезна програмка dvdisaster