This seems absurdly easy, and I have the idea I used to know how to find out, but...
On Mac Os 10.4, I want to do a raw copy from/two two devices using
dd if=*inputdev* of=*outputdev* ibs=?? obs=??. How can I tell what are the best block sizes to pass to ibs and obs?
Related information — There was a question on SO, Purpose of ibs/obs/bs in dd, with a very nice answer by Jonathan Leffler.
Postscript Looks hard, I'm afraid. From a message on the drawin-drivers list:
The problem is that the Size, and Preferred Block Size information in the IORegistry is unreliable for open session CD-R discs, and in order to provide compatibility with the widest range of devices, I need to issue a sequence of SCSI commands to the device in order to determine where the actual last written block on the disc is, and what the actual block size of the media is.
So the contents of Preferred Block Size in the IO Registry, even if it can be accessed, could be be wrong...
But a reliable method of getting this information would still be valued.