Silent errors when reading CDs

[Bill Moran]

Jean-Sebastien Roy <js at jeannot.org> wrote:
> Hi !
> 
> I'm currently using FreeBSD 4.10 on an HP D530 SFF.
> The system is perfectly stable except for the following problem 
> I'm unable to understand :
> 
> When I mount a cdrom (mount /cdrom), then calculate the MD5 hash 
> of a big file on a CD (md5 /cdrom/bigfile), the results are often random:
> unmounting, mounting again and calculating again the MD5 often result in
> a different value. What disturb me the most is that absolutely no errors
> are reported in any log (no read errors for example).
> 
> I thought the CDROM reader, a LITE-ON LTR-48327S PQS3, was the culprit, 
> so I replaced it with a PLEXTOR DVDR PX-712A and got the exact same results
> (i.e. random MD5 values). I checked the RAM using memtest and got no
> errors. The problem does not occur for files on the harddisk.
> 
> hw.ata.atapi_dma is set since both drives support it and it seems to be 
> required for proper CD/DVD burning. The CD drive is the master on its
> own ATA bus.
> 
> Could someone provide me a hint on what to check next or how to fix this
> problem ?
> 
> Thank you very much in advance,

I tried this out on my machine, which is completely different hardware/config
than yours, and I could not reproduce the problem.  It would seem to me that
the problem is either hardware-specific or the result of the above-mentioned
sysctl (my atapi_dma is turned off, and I'm too lazy to reboot to try it on)

This question may be better suited for hackers@

-- 
Bill Moran
Potential Technologies
http://www.potentialtech.com