"cp -a" not consistently reporting error on cdrom read error

[Joe Peterson]

Hi, I hope this is the correct forum in which to ask this...

I have been trying to read a particular cdrom that seems to be of
"marginal" quality.  I often get cdrom read errors reported in my
/var/log/messages file, but when these errors happen, I do not always
get an error reported from the "cp" command in coreutils - rather, the
file is just not completely copied (i.e. resulting file is too short).
This is a little disconcerting, of course.  Are there cases in which cp
would not report an error even when not writing the full file?

I am running Gentoo Linux with coreutils 6.4 and kernel
2.6.19-gentoo-r5, but the problem also happened on kernel 2.6.18.

The reason I suspect coreutils is that if I repeat the cdrom read (using
"cp -a"), producing the short file repeatedly, and then I run "rsync
-av" instead, rsync reports the read error, whereas cp did not.

Note that most of the time I *do* get an error from cp:

        cp: reading `/media/cd/co_d02/co_d02.tpc': Input/output error

But not always.  Also, when I try repeatedly, I often get the error
right away, as if the read attempt has been buffered.  I wonder if I
also get in this "buffered" state when it is not reporting the error...
 Not sure if this is related or what part of the system is doing the
buffering.

I know I have not provided a great deal of info, but I have been
unsuccessful at finding info about this, even in the coreutils
ChangeLog, and the problem is rather hard to reproduce.  Any insight or
ideas would be appreciated!

        Thanks, Joe



Here is an excerpt from /var/log/messages:

Feb 24 10:31:03 crater hdc: media error (bad sector): status=0x51 {
DriveReady S
eekComplete Error }
Feb 24 10:31:03 crater hdc: media error (bad sector): error=0x30 {
LastFailedSen
se=0x03 }
Feb 24 10:31:03 crater ide: failed opcode was: unknown
Feb 24 10:31:03 crater ATAPI device hdc:
Feb 24 10:31:03 crater Error: Medium error -- (Sense key=0x03)
Feb 24 10:31:03 crater (reserved error code) -- (asc=0x15, ascq=0x00)
Feb 24 10:31:03 crater The failed "Read 10" packet command was:
Feb 24 10:31:03 crater "28 00 00 05 12 9f 00 00 08 00 00 00 00 00 00 00"
Feb 24 10:31:03 crater end_request: I/O error, dev hdc, sector 1329788
Feb 24 10:31:03 crater Buffer I/O error on device hdc, logical block 332447
Feb 24 10:31:03 crater Buffer I/O error on device hdc, logical block 332448
Feb 24 10:31:03 crater Buffer I/O error on device hdc, logical block 332449
Feb 24 10:31:03 crater Buffer I/O error on device hdc, logical block 332450
Feb 24 10:31:03 crater Buffer I/O error on device hdc, logical block 332451
Feb 24 10:31:03 crater Buffer I/O error on device hdc, logical block 332452
Feb 24 10:31:03 crater Buffer I/O error on device hdc, logical block 332453
Feb 24 10:31:03 crater Buffer I/O error on device hdc, logical block 332454
Feb 24 10:34:45 crater hdc: cdrom_decode_status: status=0x51 {
DriveReady SeekComplete Error }
Feb 24 10:34:45 crater hdc: cdrom_decode_status: error=0x40 {
LastFailedSense=0x04 }
Feb 24 10:34:45 crater ide: failed opcode was: unknown