On Tue, Sep 25, 2012 at 10:50:44PM +0200, Kay Sievers wrote: > On Tue, Sep 25, 2012 at 10:33 PM, Francesco Turco <fturco@xxxxxxxxxxx> wrote: > > I'm trying to use fdisk (from util-linux 2.19.1) for creating a > > partition on a drive. I noticed that the start sector of the first > > partition must be at least 2048, that is 1 MiB from the beginning of the > > drive. This can be changed by entering the "expert mode" and using the > > "move beginning of data in a partition" option. But I'm still wondering > > why fdisk reserves so much space by default. > > > > As far as I know the only sector that should not be used for partitions > > is the first one, that is, sector 0. It is reserved for the MBR. So the > > first partition can start at sector 1. I read that the 1 MiB thing is > > Windows related: http://en.wikipedia.org/wiki/Logical_Disk_Manager. Or > > it's something that Linux users should also care about? I can't find a > > convincing explanation anywhere. > > > > This 1 MiB thing seems to affect parted, too, as it wants partition > > boundaries to be multiples of 1 MiB. I don't know if it's related to the > > problem I have with fdisk, though. > > It's a de-facto standard, which Windows does too. The first megabyte > is reserved here for a boot loader or any other management data that > could be needed for a disk or box to boot from. The real reason is that 1MiB is ideal offset to keep partitions aligned on almost all random hardware. This offset is compatible with 512-byte, 4096-byte sector devices, many raid devices as well as old broken WD disks where physical sector size has been incorrectly reported. You can use dd(1) to move your PT + data to another device without care about physical device topology (I/O limits), etc. It's also important to keep your partition sizes aligned to MiB -- this is for example default in fdisk if you specify the size in +<size>{M,G} convention. > Boot loader issues are probably not that interesting on EFI boxes and > other non-BIOS hardware, but on usually big sized disks it's still a > safe default. Yes. Probably the most complete docs with many references: https://ata.wiki.kernel.org/index.php/ATA_4_KiB_sector_issues 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
