On Sat, Jun 13, 2015 at 10:52:04PM +0800, Tom Yan wrote: > As I have mentioned in previous mails, I have an sata/usb3 adapter > which could work in uas mode, and when it does, it has a weird optimal > i/o size: > > Disk /dev/sdb: 74.5 GiB, 80026361856 bytes, 156301488 sectors > Units: sectors of 1 * 512 = 512 bytes > Sector size (logical/physical): 512 bytes / 512 bytes > I/O size (minimum/optimal): 512 bytes / 33553920 bytes This is no problem (33553920 % 512 = 0) with the current kernel and the current util-linux git tree where we support non power of 2 alignment. > http://www.linuxquestions.org/questions/linux-newbie-8/how-to-foramt-2tb-external-hard-drive-4175529792/ > > In the above link, there shows another similar case of an external > drive with 4k physical sector. from the link: Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 33553920 bytes this is problem (33553920 % 4096 != 0) and frankly it seems like pretty strange thing, maybe kernel guys can comment it (CC: to Martin). > I am not sure if there's anything wrong with the device(s) or the > kernel, but anyway I doubt if fdisk should determine alignment with > this size. As you can calculate, it may not necessarily be a multiple > of the size of physical sectors, or that of common erase block of SSDs > (which is not reported anywhere AFAIK). > > Perhaps this I/O size does matter on alignment for certain cases, but > shouldn't physical sector or erase block be at least of higher > priority when it comes to alignment? I think we can test "optimal_io_size % physical_sector_size" and use physical sector size as the granularity if the optimal_io_size is a strange number. > In any case, it would be nice if fdisk can allow customize alignment > (like gdisk does), so that users can at least decide how partitions > should be aligned in weird cases like this. With that, the long-time > deprecated "dos compatibility" might be able to go as well. I'll think about it... Karel -- Karel Zak <kzak@xxxxxxxxxx> http://karelzak.blogspot.com -- To unsubscribe from this list: send the line "unsubscribe util-linux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
