Re: ATA 4 KiB sector issues.

[Tejun Heo]

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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