On Mon, Aug 17, 2015 at 10:46 PM, <Valdis.Kletnieks@xxxxxx> wrote: > On Mon, 17 Aug 2015 16:35:59 +0530, Navin P said: >> Hi, >> Why is SECTOR_SIZE 512 ? > > Because most fixed-block devices presented a logical interface in terms > of 512 byte sectors. (IBM's count-key-data format is an example of a non-fixed > block device). > >> Is it going to change or is it cast in stone ? > > As you have probably figured out, high-capacity devices have often moved > to 4K physical blocks to avoid wasting so much room between blocks (the hardware > format includes a preamble to each block and a postamble, and dead space in > between, it uses more space than you think). > > However, as long as there are still devices out there that have 512 byte > blocks, it's not changing. And it still won't change unless there's a > good reason to change it (hint - how many places in the kernel have hidden > assumptions about the size of SECTOR_SIZE being 9 bits worth?) I posted this to http://www.mail-archive.com/linux-kernel@xxxxxxxxxxxxxxx/msg956881.html avoided cross posting. Looks like this is cast in stone at kernel . I was thinking of doing sectors written * hw_sector_size. But the sectors counters in /proc/diskstats are actually 512 byte sections even for 4kN disks. That way userspace programs are immune to underlying sector. Wish that page_size was also same :) There are lot of places like 9 bits . http://lxr.free-electrons.com/source/block/blk-lib.c bio->bi_iter.bi_size = req_sects << 9; http://lxr.free-electrons.com/source/include/linux/blkdev.h sprinkled with 9 . I'm assuming the magic number 9 here is SECTOR_SIZE. :) The hw_sector_size must be cosmetic in that sense or just to you tell you that "your drive really is 4kn" or "512e". _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
