On Sat, 13 Nov 2004, Alan Cox wrote: > > 1) It's the read ahead that causes the problem. If one use > > hdparm and set the read ahead to 0 on the device, then I have > > no problem to verify a cd using dd. > > Correct So, why not set read ahead to 0 during the install process (or at least during the media check). It's also strange that the media check works for some people. I don't see anything here that depends on the hardware except perhaps hardware that does not support dma at all (blacklisted), or that does not use ide-cd. Maybe it's the combination of slow CPU and fast cd-rom that makes it perform more read ahead and increase the chance of generating an error (yet another guess :-). > The "end" of a CD-R is undefined for about 150K. ide-scsi correctly > retries errors at the disk end and reduces the disk size based on the > error position. ide-cd doesn't. If the layer above can tell ide-cd where the end is then it will never need to seek past that. For an iso fs the size is known and I guessed in the previous mail that this size was passed in to ide-cd when you mount it. A retry to find the real end of course would also solve it. I don't know that much about cdroms so I can't say I know anything about the "end is undefined for 150K" part. I played with different padding sizes, but that didn't alter the end position. The full track I could read back in was of constant size no matter what padding I tried. Well, I feel a lot better now that I know what the problem is. I hate problems where I don't know the technical reason behind it. Thanks. -- /Dennis Björklund
