On Mar 7, 2011, at 11:03 PM, Chris Murphy wrote: > > > On Mar 7, 2011, at 8:25 PM, Milo Velimirović wrote: > >> >> On Mar 7, 2011, at 7:06 PM, Chris Murphy wrote: >> >>> >>> On Mar 7, 2011, at 6:02 PM, Markus Hitter wrote: >>> >>>> >>>> Am 07.03.2011 um 20:22 schrieb Chris Murphy: >>>> >>>>> I don't know the difference with XNU between block level and raw device >>>> >>>> For reading the whole thing, the result should be the same for both. A >>>> "cmp", "diff" or two "md5" should tell you wether I'm speaking the truth >>>> ;-) >>> >>> >>> I agree. Should be the same for both with respect to performance as well, >>> but they aren't. 6x slower for block level compared to raw. >> >> Yes, the resulting files should be the same; no, the copy should not be the >> same speed! It's hard for me to believe that this confusion about block vs. >> character/raw devices still exists when UNIX is more than 40 years old. > > OK well, then it should be simple for you to explain why /dev/disk0 results > in 17MB/s read, and /dev/rdisk0 results in 107MB/s read, and on Linux > /dev/sda result in 107MB/s read which is the block level device and there is > no raw device created anymore.
I can't speak for Linux, though it would appear based on your performance numbers that the block and raw devices were unified using the raw model. Historically, in the UNIX world, block devices had I/O done (surprise!) block at a time into a set of kernel maintained buffers and data was copied to/from the disk buffer cache from/to user space. Raw access bypassed this disk cacheing/buffer mechanism. - Milo _______________________________________________ MacOSX-admin mailing list [email protected] http://www.omnigroup.com/mailman/listinfo/macosx-admin
