short read from CD-RW

[Dan Strick]

I just wrote an iso image to a virgin CD-RW with the following command:

	burncd -f /dev/acd0c -s 24 data 5.2.1-RC-i386-disc1.iso fixate

and the burncd program said:

	next writeable LBA 0
	writing from file 5.2.1-RC-i386-disc1.iso size 657024 KB
	written this track 657024 KB (100%) total 657024 KB
	fixating CD, please wait..

which is consistent with the iso image file size = 672792576 bytes =
657024 KB = 328512 2KB records.  When I read the data back in from
the CD with this command:

	dd if=/dev/acd0c of=xxx bs=2k

the dd program says:

	dd: /dev/acd0c: Input/output error
	328510+0 records in
	328510+0 records out
	672788480 bytes transferred in 252.669511 secs (2662721 bytes/sec)

which is consistent with the xxx file size = 672788480 bytes = 328510
2KB records.  Note that this is 4KB short of the expected file size.
The acd driver produced this error message on the console:

	acd0: READ_BIG - MEDIUM ERROR asc=0x11 ascq=0x05 error=0x00

Recent SCSI standards further explain asc=0x11 ascq=0x05 as meaning
"L-EC UNCORRECTABLE ERROR" and "L-EC" as "Layered Error Correction".

I don't believe for a second that my CD medium just happened to have
a bad sector at the very end of the iso disk image.  Could this be a
hardware glitch?  Could the error message be incorrect?
Is a driver bug involved?

Notes:
  1) I am running FreeBSD 4.9-RELEASE.
  2) The CD-writer is a SAMSUNG SM-352B.
  3) I get similar errors (not sure of the ascq) when any of my CD drives
     (both ATA and SCSI) try to read the first blank sector at the end of
     a CD-R (should be a short read or EOF).

Dan Strick
strick at covad.net