1) stat(2), the st_blksize field in the stat struct 2) no, because it's the device, not dd, that's not letting it work. CD-ROMS only want to output 2K of data at a time, so if you request less than that, they just won't do it. Generally though, most devices will output less than st_blksize, but it'll just go damn slow.
Jason On 5/31/06, akonsu <[EMAIL PROTECTED]> wrote:
thanks everybody. 1. how do i determine the corect block size for a device? 2. is the fact that dd does not work without any bs parameter a bug and should be reported? thanks konstantin try > dd if=/dev/rcd0c of=disk.iso bs=32k > > note the "rcd0c" instead of "cd0a". The 'a' vs. 'c' doesn't (seem to) > matter, I just philosophically prefer the 'c' implying entire disk, > rather than just one partition. The "raw" mode of access makes a lot of > difference here. > > I put the "bs=32k" in there for a bit of additional performance, but it > turns out that without the "bs=" line, it didn't work at all. After a > little thought (and testing), I remembered that on most modern > platforms, CDROM drives have a 2k block size, so apparently dd has > trouble moving 512 bytes at a time out of CDROM drives. I confirmed > that "bs=2k" worked, "bs=1k" does not, so I might possibly be not > totally wrong on that. "bs=32k" seemed to go about twice as fast as > "bs=2k". > > Well, I learned something. :) > > Nick.
