Re: dd cdrom error

[Leung Yau Wai <chris@gist.q-station.net>]

On Thu, 27 Dec 2001, Douglas Gilbert wrote:

> Leung Yau Wai <chris@gist.q-station.net> wrote:
> > I come across a problem which seem exist in kernel 
> > 2.4.x but not in 2.2.x.
> >
> > The problem is that, when I try to using dd to create 
> > a ISO image of a cdrom then around dumping the end of 
> > the disc it will give out the following error message:
> >
> > e.g. dd if=/dev/cdrom of=n.iso
> 
> If dd is used like that, it is surprising you do not get
> more errors. An iso9660 image does not necessarily fill
> the track. So the IDE equivalent of the SCSI READ CAPACITY 
> command will often report a size that includes unwritten 
> sectors at the end. Those unwritten sectors can/will cause
> IO errors when an attempt is made to read them.
> 
> A very useful program called "isosize" has made a return to
> util-linux-2.10s (and later). Execute:
>   isosize -x /dev/cdrom
> to find the number of sectors and the sector size of the iso9660
> fs held _within_ the first track. Then use those numbers as the 
> "count=" and "bs=" arguments to dd respectively.
> 
> 
> If you still have problems try turning DMA off via hdparm
> or set the DMA mode back to 33 MHz (-X34).

	So, why problem will be happened when using DMA?

	Do you mean when not using DMA then the sectors at the end of the
disc will be auto-filled (padded)? ( I think it is impossible )

	BTW, why kernel 2.2.X will success create the ISO image of the
same disc with the same command?

	Thx your reply!