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    SubjectRe: ATA 4 KiB sector issues.
    Hello,

    On 03/09/2010 04:58 AM, Karel Zak wrote:
    >> Tejun> Reportedly, commonly used partitioners aren't ready to handle
    >> Tejun> drives larger than 2 TiB in any configuration and alignment isn't
    >
    > The limit is specific for DOS partition table (with 512-byte log.
    > sectors), but for example GPT uses 64-bit LBA. I believe that our
    > partitioning tools don't introduce any other restriction.

    Hmmm... the 'reportedly' was from Daniel Taylor or maybe I just
    misinterpreted the conversation. Daniel, can you please fill in?

    >> Tejun> done properly for drives with 4 KiB physical sectors. 4 KiB
    >> Tejun> logical sector support is broken in both the kernel
    >>
    >> Huh, what? My homedir is on a 4KiB LBS/PBS drive and has been for ~2
    >> years.

    By default, they aren't aligned properly, are they?

    >> Tejun> (need more details and probably a whole section on partitioner
    >> Tejun> behaviors)
    >>
    >> I'm Cc:'ing Karel Zak and Jim Meyering who have been doing all the
    >> alignment work for fdisk and parted respectively. Karel, Jim: The full
    >> writeup is here:
    >>
    >> http://ata.wiki.kernel.org/index.php/ATA_4_KiB_sector_issues
    >>
    >> It'd be great if you guys could share what you have been doing to the
    >> tooling.
    >
    > small summary:
    >
    > - libblkid provides unified API to topology information, it supports:
    > - ioctls (kernel >= 2.6.32)
    > - sysfs (kernel >= 2.6.31)
    > - stripe chunk size and stripe width for DM, MD. LVM and evms on
    > old kernels
    > - libparted and fdisk are linked against libblkid
    >
    > - fdisk supports 4KiB logical sector size (util-linux-ng >= 2.15
    > - fdisk supports 4KiB physical sector size (util-linux-ng >= 2.17)
    > - fdisk uses 1MiB alignment (or more if optimal I/O size is bigger)
    > and alignment_offset for all partitions in non-DOS mode
    > (util-linux-ng >= 2.17.1)

    That's great. Daniel, maybe you were testing older versions? Or
    maybe those failures were manifested from libata mishandling 4KiB r/w
    requets.

    > - parted supports 4KiB physical sector size
    > - parted uses 1MiB alignment for disks with unknown topology, disks
    > with topology information are aligned to optimal (or minimum) I/O
    > size (parted >= 2.1)

    This will result in incorrect alignment for drives which lie about the
    physical sector size to work around BIOS/drivers issues (C-1). It
    would probably be best to align to at least 1MiB.

    > - EFI GPT code in the kernel has been updated to works properly with
    > 4KiB sectors (kernel >= 2.6.33)

    libata is broken for logical 4KiB ATA devices tho. I'll fix it up.

    > - mkfs.{ext,xfs,gfs2,ocfs2} have been update to work properly with
    > topology information, mkfs.{ext,xfs} are linked against libblkid
    > for compatibility with old kernel (for stripe chunk size / width)
    >
    > - Fedora-13/RHEL6 installer uses libparted with 4KiB support
    >
    > - alignment_offset & 4KiB support is planned for LUKS (cryptsetup)
    >
    >> Tejun> Unfortunately, the transition to 4 KiB sector size, physical only
    >> Tejun> or logical too, is looking fairly ugly. Hopefully, a reasonable
    >> Tejun> solution can be reached in not too distant future but even with
    >> Tejun> all the software side updated, it looks like it's gonna cause
    >> Tejun> significant amount of confusion and frustration.
    >>
    >> With regards to XP compatibility I don't think we should go too much out
    >> of our way to accommodate it. XP has been disowned by its master and I
    >> think virtualization will take care of the rest.

    Yeah, good point. I'm just a bit worried that it might generate a lot
    of frustrated bug reports. Well, maybe we should just advise users to
    install windows first and then install Linux.

    >> FWIW, recent fdisk has a command line flag that will enable/disable DOS
    >> compatible layout.
    >
    > yes, util-linux-ng 2.17.1, fdisk -c
    >
    > Note that non-DOS mode will be default in the next major
    > util-linux-ng release.

    I'll try to merge these information into the ata-4k doc.

    Thank you very much.

    --
    tejun


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