Re: ATA support for 4k sector size

Re: ATA support for 4k sector size

[Andries E. Brouwer]

Ha, a discussion about partitions and disk geometry.

Greg Freemyer wrote: 
> If the reported geometry of these drives was changed to have sectors /
> track be a multiple of 8, wouldn't that fix most of the issues.

It is almost twenty years ago that disks stopped having a geometry.
The ATA standard tells disks over 8 GB to report their geometry as
16383/16/63. That is, there is no information in what is reported.
It is just a constant to satisfy ancient software.

Andries

ATA support for 4k sector size

[Matthew Wilcox]

The two patches following this add support for drives which have sector
sizes other than 512 bytes.  I haven't been able to test this as I don't
have the hardware.

Individual host drivers will have to be updated to support sizes other
than 512 bytes.

Support for logical sector sizes that differ from physical sector sizes
depends on the READ CAPACITY 16 patch I posted in December that isn't in
scsi-misc yet.

The approach I've taken to generating the tables of which commands need
a 512-byte transfer size and which use the drive's sector size command is
'innovative'.  Review is encouraged ;-)

Re: ATA support for 4k sector size

[H. Peter Anvin]

Matthew Wilcox wrote:
> The two patches following this add support for drives which have sector
> sizes other than 512 bytes.  I haven't been able to test this as I don't
> have the hardware.
> 
> Individual host drivers will have to be updated to support sizes other
> than 512 bytes.
> 
> Support for logical sector sizes that differ from physical sector sizes
> depends on the READ CAPACITY 16 patch I posted in December that isn't in
> scsi-misc yet.
> 
> The approach I've taken to generating the tables of which commands need
> a 512-byte transfer size and which use the drive's sector size command is
> 'innovative'.  Review is encouraged ;-)

What sector size do we report to user space for this?  I'm asking 
because logical sector size is visible in most partition formats.

	-hpa

Re: ATA support for 4k sector size

[Martin K. Petersen]

>>>>> "hpa" == H Peter Anvin <hpa@zytor.com> writes:

>> The two patches following this add support for drives which have
>> sector sizes other than 512 bytes.  I haven't been able to test this
>> as I don't have the hardware.

hpa> What sector size do we report to user space for this?  I'm asking
hpa> because logical sector size is visible in most partition formats.

There are several flavors of drives we have to deal with:

512-byte logical / 512-byte hardware (current)
512-byte logical / 4096-byte hardware (ATA, doing read-modify-write)
4096-byte logical / 4096-byte hardware (SCSI initially, ATA later)

Because of 63-sector legacy problems a bunch of ATA vendors will
initially ship 512/4096 drives that are not naturally aligned.
I.e. logical sector 63 will be aligned on a 4KB hardware sector
boundary to overcome the misaligned default partitioning.

I have been working on some alignment patches the last week.  They hook
into the stuff Matthew has been doing in libata and I'll post them
shortly.

For each block device you'll get a hardware sector size exposed as well
as whether the device (partition) is naturally aligned or not.  This
works for both ATA and SCSI devices.

I'll defer to people like yourself for how this needs to work wrt. boot
loaders and creating partition tables.  I'm CC:ing Eric Sandeen because
he's also looking at this...

-- 
Martin K. Petersen	Oracle Linux Engineering

Re: ATA support for 4k sector size

[H. Peter Anvin]

Martin K. Petersen wrote:
> 
> I'll defer to people like yourself for how this needs to work wrt. boot
> loaders and creating partition tables.  I'm CC:ing Eric Sandeen because
> he's also looking at this...
> 

I wish it was left to people like myself.  Realistically when it comes 
to disks with 4096-byte logical sectors it going to matter how the 
firmware chooses to expose it.

Most likely, the universe will explode at this time, since very few 
bootloaders can deal with a sector size other than 512 bytes, and 
virtually every partition table format contains a sector size 
dependency, which also means you'll break any mechanical imaging solution.

It's going to hurt :(

	-hpa

Re: ATA support for 4k sector size

[Martin K. Petersen]

>>>>> "hpa" == H Peter Anvin <hpa@zytor.com> writes:

hpa> I wish it was left to people like myself.  Realistically when it
hpa> comes to disks with 4096-byte logical sectors it going to matter
hpa> how the firmware chooses to expose it.

Well. In the short term ATA is going to emulate 512 (at a penalty for
misaligned I/O).  SCSI is switching to 4KB wholesale.

I have a 4KB/4KB drive here that I have had fun booting from the last
few days.


hpa> Most likely, the universe will explode at this time, since very few
hpa> bootloaders can deal with a sector size other than 512 bytes, and
hpa> virtually every partition table format contains a sector size
hpa> dependency, which also means you'll break any mechanical imaging
hpa> solution.

hpa> It's going to hurt :(

Yep, it sucks :|

-- 
Martin K. Petersen	Oracle Linux Engineering

Re: ATA support for 4k sector size

[Karel Zak]

On Wed, Feb 25, 2009 at 03:33:46PM -0800, H. Peter Anvin wrote:
> virtually every partition table format contains a sector size  
> dependency

 Is it true that "every partition table format"? I see in
 fs/partitions/ that only ibm.c and msdos.c care about a sector size.
 It seems that the others formats are based on 512 sectors only.

    Karel

-- 
 Karel Zak  <kzak@redhat.com>

Re: ATA support for 4k sector size

[H. Peter Anvin]

Karel Zak wrote:
> On Wed, Feb 25, 2009 at 03:33:46PM -0800, H. Peter Anvin wrote:
>> virtually every partition table format contains a sector size  
>> dependency
> 
>  Is it true that "every partition table format"? I see in
>  fs/partitions/ that only ibm.c and msdos.c care about a sector size.
>  It seems that the others formats are based on 512 sectors only.
> 

And do they do so correctly?

Looking at the UEFI spec for one, the GPT partition table format
definitely has a logical sector size dependency.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

Re: ATA support for 4k sector size

[H. Peter Anvin]

Martin K. Petersen wrote:
> 
> Because of 63-sector legacy problems a bunch of ATA vendors will
> initially ship 512/4096 drives that are not naturally aligned.
> I.e. logical sector 63 will be aligned on a 4KB hardware sector
> boundary to overcome the misaligned default partitioning.
> 

I was under the impression Vista didn't do this?  Is there any way to 
force these drives into a sane mode (at the expense of a total data loss)?

	-hpa

Re: ATA support for 4k sector size

[Martin K. Petersen]

>>>>> "hpa" == H Peter Anvin <hpa@zytor.com> writes:

>> Because of 63-sector legacy problems a bunch of ATA vendors will
>> initially ship 512/4096 drives that are not naturally aligned.
>> I.e. logical sector 63 will be aligned on a 4KB hardware sector
>> boundary to overcome the misaligned default partitioning.
>> 

hpa> I was under the impression Vista didn't do this?  Is there any way
hpa> to force these drives into a sane mode (at the expense of a total
hpa> data loss)?

Modern Windows aligns the first partition on a 1 MB boundary.

As far as disks go, initially the plan was to have "legacy" branded
drives with 63-sector alignment.  But I think that has been abandoned in
favor of instant one-time formatting.  I.e. you can pick your poison
*once* and that formatting will be done in constant time.  Any
subsequent changes to blocking and alignment will require a real
low-level format.

That's all fine and dandy if you go down and buy a drive a Fry's and
you're the first to use it.  But we don't have that luxury on systems
that come preinstalled with Windows.  In that case we have to deal with
whatever the OEM decided during manufacturing.

IOW, we have to deal with all the possible configurations.

-- 
Martin K. Petersen	Oracle Linux Engineering

Re: ATA support for 4k sector size

[H. Peter Anvin]

Martin K. Petersen wrote:
> 
> Modern Windows aligns the first partition on a 1 MB boundary.
> 
> As far as disks go, initially the plan was to have "legacy" branded
> drives with 63-sector alignment.  But I think that has been abandoned in
> favor of instant one-time formatting.  I.e. you can pick your poison
> *once* and that formatting will be done in constant time.  Any
> subsequent changes to blocking and alignment will require a real
> low-level format.
> 

Why one-time?

	-hpa

Re: ATA support for 4k sector size

[Martin K. Petersen]

>>>>> "hpa" == H Peter Anvin <hpa@zytor.com> writes:

hpa> Martin K. Petersen wrote:
>> 
>> Modern Windows aligns the first partition on a 1 MB boundary.
>> 
>> As far as disks go, initially the plan was to have "legacy" branded
>> drives with 63-sector alignment.  But I think that has been abandoned
>> in favor of instant one-time formatting.  I.e. you can pick your
>> poison *once* and that formatting will be done in constant time.  Any
>> subsequent changes to blocking and alignment will require a real
>> low-level format.
>> 

hpa> Why one-time?

It's a compromise to avoid hours of low-level formatting before you can
use a drive.  New drives will come from the factory formatted in a
special way that can be switched instantaneously.  But once you start
writing you're stuck with it.

-- 
Martin K. Petersen	Oracle Linux Engineering

Re: ATA support for 4k sector size

[H. Peter Anvin]

Martin K. Petersen wrote:
> 
> hpa> Why one-time?
> 
> It's a compromise to avoid hours of low-level formatting before you can
> use a drive.  New drives will come from the factory formatted in a
> special way that can be switched instantaneously.  But once you start
> writing you're stuck with it.
> 

That's ridiculously stupid.  All you need is an offset parameter, which 
can be flipped at will.  Now, flipping it will obviously scramble all 
data, but there is absolutely no reason why it shouldn't be possible to 
instantaneously flip it back and forth.

	-hpa

Re: ATA support for 4k sector size

[Martin K. Petersen]

>>>>> "hpa" == H Peter Anvin <hpa@zytor.com> writes:

hpa> That's ridiculously stupid.  All you need is an offset parameter,
hpa> which can be flipped at will.  Now, flipping it will obviously
hpa> scramble all data, but there is absolutely no reason why it
hpa> shouldn't be possible to instantaneously flip it back and forth.

I'm just quoting what I was told a few months ago.  I'm not
participating in IDEMA and for all I know that approach could have
changed again.

I'll ask one of my contacts to find out what the current status is...

-- 
Martin K. Petersen	Oracle Linux Engineering

Re: ATA support for 4k sector size

[david]

On Wed, 25 Feb 2009, Martin K. Petersen wrote:

>>>>>> "hpa" == H Peter Anvin <hpa@zytor.com> writes:
>
>>> The two patches following this add support for drives which have
>>> sector sizes other than 512 bytes.  I haven't been able to test this
>>> as I don't have the hardware.
>
> hpa> What sector size do we report to user space for this?  I'm asking
> hpa> because logical sector size is visible in most partition formats.
>
> There are several flavors of drives we have to deal with:
>
> 512-byte logical / 512-byte hardware (current)
> 512-byte logical / 4096-byte hardware (ATA, doing read-modify-write)
> 4096-byte logical / 4096-byte hardware (SCSI initially, ATA later)

add to this good support for SSDs

?? logical / 128K hardware

or similar.

David Lang

> Because of 63-sector legacy problems a bunch of ATA vendors will
> initially ship 512/4096 drives that are not naturally aligned.
> I.e. logical sector 63 will be aligned on a 4KB hardware sector
> boundary to overcome the misaligned default partitioning.
>
> I have been working on some alignment patches the last week.  They hook
> into the stuff Matthew has been doing in libata and I'll post them
> shortly.
>
> For each block device you'll get a hardware sector size exposed as well
> as whether the device (partition) is naturally aligned or not.  This
> works for both ATA and SCSI devices.
>
> I'll defer to people like yourself for how this needs to work wrt. boot
> loaders and creating partition tables.  I'm CC:ing Eric Sandeen because
> he's also looking at this...
>
>

Re: ATA support for 4k sector size

[Martin K. Petersen]

>>>>> "david" == david  <david@lang.hm> writes:

>> 512-byte logical / 512-byte hardware (current) 512-byte logical /
>> 4096-byte hardware (ATA, doing read-modify-write) 4096-byte logical /
>> 4096-byte hardware (SCSI initially, ATA later)

david> add to this good support for SSDs

david> ?? logical / 128K hardware

david> or similar.

Yep.  And that goes for RAID arrays too.

For SCSI there some knobs we can query to get this information and my
alignment changes are using those (and they are in turn what Willy's
stuff hooks into).

I've been lobbying the SSD vendors whose architecture is prone to
misalignment problems to propose a similar set of knobs for ATA.  But so
far it's just been a lot of talking.

My topology changes are a bit abstract in the sense that they expose:

 - smallest I/O you can submit without incurring a penalty (hw sector,
   raid chunk size)

 - optimal I/O size for the device in question

 - biggest I/O you can submit without incurring a penalty

 - alignment

We can use these parameters to lay out partitions and filesystems
optimally.  Just like we currently do with XFS but implemented in a more
generic way that all filesystems can use.

-- 
Martin K. Petersen	Oracle Linux Engineering

Re: ATA support for 4k sector size

[david]

On Wed, 25 Feb 2009, Martin K. Petersen wrote:

>>>>>> "david" == david  <david@lang.hm> writes:
>
>>> 512-byte logical / 512-byte hardware (current) 512-byte logical /
>>> 4096-byte hardware (ATA, doing read-modify-write) 4096-byte logical /
>>> 4096-byte hardware (SCSI initially, ATA later)
>
> david> add to this good support for SSDs
>
> david> ?? logical / 128K hardware
>
> david> or similar.
>
> Yep.  And that goes for RAID arrays too.
>
> For SCSI there some knobs we can query to get this information and my
> alignment changes are using those (and they are in turn what Willy's
> stuff hooks into).
>
> I've been lobbying the SSD vendors whose architecture is prone to
> misalignment problems to propose a similar set of knobs for ATA.  But so
> far it's just been a lot of talking.

even if we can't get them to give us any info from the drive directly, we 
still want to allow the sysadmin to configure the use of the systems when 
they can find the info in other ways.

> My topology changes are a bit abstract in the sense that they expose:
>
> - smallest I/O you can submit without incurring a penalty (hw sector,
>   raid chunk size)
>
> - optimal I/O size for the device in question
>
> - biggest I/O you can submit without incurring a penalty
>
> - alignment
>
> We can use these parameters to lay out partitions and filesystems
> optimally.  Just like we currently do with XFS but implemented in a more
> generic way that all filesystems can use.

if you have the smallest and largest I/O you can submit without a penalty 
and the alignment, isn't the optimal I/O size everything between these 
two? (or at least everything between these two may be close enough that 
defining an 'optimal' size may not be worthwhile)

David Lang

Re: ATA support for 4k sector size

[Martin K. Petersen]

>>>>> "david" == david  <david@lang.hm> writes:

david> even if we can't get them to give us any info from the drive
david> directly, we still want to allow the sysadmin to configure the
david> use of the systems when they can find the info in other ways.

You can specify RAID parameters on the mkfs.xfs command line today.
mke[234]fs have similar knobs.


david> if you have the smallest and largest I/O you can submit without a
david> penalty and the alignment, isn't the optimal I/O size everything
david> between these two? (or at least everything between these two may
david> be close enough that defining an 'optimal' size may not be
david> worthwhile)

These parameters come straight out of SCSI.  I described them wrong.
maximum is the biggest I/O the device can handle, full stop.  Optimal is
the preferred I/O size for the array.

-- 
Martin K. Petersen	Oracle Linux Engineering

Re: ATA support for 4k sector size

[Theodore Tso]

On Wed, Feb 25, 2009 at 06:27:18PM -0500, Martin K. Petersen wrote:
> 
> Because of 63-sector legacy problems a bunch of ATA vendors will
> initially ship 512/4096 drives that are not naturally aligned.
> I.e. logical sector 63 will be aligned on a 4KB hardware sector
> boundary to overcome the misaligned default partitioning.
> 

Are we *sure* that this is what they plan to be doing?  Is there a way
we can query the hardware to find out for sure what drives are doing
what?

I'll note that Vista starts all new partitions at the 1MB boundary, so
its filesystems will be naturally aligned.  As I mentioned in a recent blog
entry:

http://thunk.org/tytso/blog/2009/02/20/aligning-filesystems-to-an-ssds-erase-block-size/

... this is one place Vista is ahead of Linux.  So while Microsoft's
market share has slipped, 85% of all new x86 machines still have some
variant of Redmond-spawn installed on them, and with the advent of
Windows 7 coming soon, and Microsoft making it harder and harder for
vendors to ship machines upgraded to Windows XP, it
seems... surprising... that new disks meant for Windows Vista or
Windows 7 systems would be misaligned to start at logical sector 63.

						- Ted

Re: ATA support for 4k sector size

[Martin K. Petersen]

>>>>> "Ted" == Theodore Tso <tytso@mit.edu> writes:

>> Because of 63-sector legacy problems a bunch of ATA vendors will
>> initially ship 512/4096 drives that are not naturally aligned.
>> I.e. logical sector 63 will be aligned on a 4KB hardware sector
>> boundary to overcome the misaligned default partitioning.
>> 

Ted> Are we *sure* that this is what they plan to be doing?  

I have asked my contacts to verify.  That was the plan as of last
October.


Ted> Is there a way we can query the hardware to find out for sure what
Ted> drives are doing what?

Yep.  And with my patches the appropriate alignment is exposed in sysfs
for each block device.

Hardware workarounds for DOS partition table brain damage have existed
for a long time.  On a lot of RAID arrays you have to pick a LUN
personality.  And by choosing DOS/Windows/Linux you often align sector
63 to the internal RAID chunk size.

I'm working with several RAID vendors to make sure they set the right
alignment offset when they do that.  That isn't currently the case.  The
alignment knobs only recently made their appearance in the spec to
accommodate the 4KB sector transition.


Ted> I'll note that Vista starts all new partitions at the 1MB boundary,
Ted> so its filesystems will be naturally aligned.

Maybe.  See above.

-- 
Martin K. Petersen	Oracle Linux Engineering

Re: ATA support for 4k sector size

[Matthew Wilcox]

On Wed, Feb 25, 2009 at 09:50:43PM -0500, Theodore Tso wrote:
> On Wed, Feb 25, 2009 at 06:27:18PM -0500, Martin K. Petersen wrote:
> > Because of 63-sector legacy problems a bunch of ATA vendors will
> > initially ship 512/4096 drives that are not naturally aligned.
> > I.e. logical sector 63 will be aligned on a 4KB hardware sector
> > boundary to overcome the misaligned default partitioning.
> 
> Are we *sure* that this is what they plan to be doing?  Is there a way
> we can query the hardware to find out for sure what drives are doing
> what?

The drive I have that's pretending to be a 512/4k drive reports this:

$ sudo sg_readcap -l /dev/sdc
Read Capacity results:
   Protection: prot_en=0, p_type=0
   Last logical block address=625142447 (0x2542eaaf), Number of logical blocks=625142448
   Logical block length=512 bytes
   Logical blocks per physical block=3 (log base 2) [actual=8]
   Lowest aligned logical block address=0
Hence:
   Device size: 320072933376 bytes, 305245.3 MiB, 320.07 GB

This disagrees with Martin's assertion.

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."

Re: ATA support for 4k sector size

[Martin K. Petersen]

>>>>> "Matthew" == Matthew Wilcox <matthew@wil.cx> writes:

Matthew> Lowest aligned logical block address=0

Matthew> This disagrees with Martin's assertion.

The original roadmap was to transition to 4KB sectors in 2006,
coinciding with the Vista release.

Given how long this has taken (we're now talking ~2011 for GA) it may
very well be that the alignment knobs will be unused because everybody
will be using Vista or 7 by then.

That doesn't change the RAID array alignment problem, however.  And we
need to prepare our partitioning tools to align correctly regardless.

-- 
Martin K. Petersen	Oracle Linux Engineering

Re: ATA support for 4k sector size

[James Andrewartha]

Martin K. Petersen wrote:
>>>>>> "Matthew" == Matthew Wilcox <matthew@wil.cx> writes:
> 
> Matthew> Lowest aligned logical block address=0
> 
> Matthew> This disagrees with Martin's assertion.
> 
> The original roadmap was to transition to 4KB sectors in 2006,
> coinciding with the Vista release.
> 
> Given how long this has taken (we're now talking ~2011 for GA) it may
> very well be that the alignment knobs will be unused because everybody
> will be using Vista or 7 by then.

The plan does seem to have changed - WD's shipping 4k sector drives that are 
sane and require a drive jumper or tool for WinXP and old cloning utilities.

http://techreport.com/discussions.x/18115
http://wdc.com/en/products/advancedformat/
http://www.wdc.com/wdproducts/library/whitepapers/en/2579-771430-A00.pdf

-- 
James Andrewartha

Re: ATA support for 4k sector size

[H. Peter Anvin]

On 12/10/2009 11:05 PM, James Andrewartha wrote:
> Martin K. Petersen wrote:
>>>>>>> "Matthew" == Matthew Wilcox <matthew@wil.cx> writes:
>>
>> Matthew> Lowest aligned logical block address=0
>>
>> Matthew> This disagrees with Martin's assertion.
>>
>> The original roadmap was to transition to 4KB sectors in 2006,
>> coinciding with the Vista release.
>>
>> Given how long this has taken (we're now talking ~2011 for GA) it may
>> very well be that the alignment knobs will be unused because everybody
>> will be using Vista or 7 by then.
> 
> The plan does seem to have changed - WD's shipping 4k sector drives that
> are sane and require a drive jumper or tool for WinXP and old cloning
> utilities.
> 
> http://techreport.com/discussions.x/18115
> http://wdc.com/en/products/advancedformat/
> http://www.wdc.com/wdproducts/library/whitepapers/en/2579-771430-A00.pdf
> 

Even more important, the alignment can be changed as opposed to being
fixed for the manufacture of the disk.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

Re: ATA support for 4k sector size

[Martin K. Petersen]

>>>>> "James" == James Andrewartha <jamesa@daa.com.au> writes:

>> Given how long this has taken (we're now talking ~2011 for GA) it may
>> very well be that the alignment knobs will be unused because
>> everybody will be using Vista or 7 by then.

James> The plan does seem to have changed - WD's shipping 4k sector
James> drives that are sane and require a drive jumper or tool for WinXP
James> and old cloning utilities.

The disk vendors have agreed to transition no later than 2011.  There
are definitely drives coming out with 4KB physical blocks before then.

There has been a lot of discussion of the merits of shipping 1-aligned
drives by default given that Vista and Windows 7 handle alignment
correctly.

I don't think there has been any firm decisions in IDEMA wrt. 0
vs. 1-aligned.  It may be up to each vendor's discretion, target market
segment, etc.

-- 
Martin K. Petersen	Oracle Linux Engineering

Re: ATA support for 4k sector size

[Martin K. Petersen]

>>>>> "Matthew" == Matthew Wilcox <matthew@wil.cx> writes:

Matthew> Lowest aligned logical block address=0

Matthew> This disagrees with Martin's assertion.

Quick answer from one of my contacts.  Desktop drives will indeed ship
with an alignment of 1(*).  The alignment is hardwired at time of
manufacture and can't be changed.

(*) I had to go back and reread the ATA spec to grok this.  READ
CAPACITY(16) indicates the lowest naturally aligned LBA.  With LBA 63
offset in play that would be LBA 7.

ATA, on the other hand, indicates how much LBA 0 is offset from the
beginning of the first physical sector.  If LBA 63 is naturally aligned
that means that LBA 0 is offset 512 bytes (physical sector 0 starts at
LBA -1 if you will). Hence IDENTIFY DEVICE word 209 will contain 0x4001.

So you need to tweak your RC16 response a bit...

-- 
Martin K. Petersen	Oracle Linux Engineering

Re: ATA support for 4k sector size

[Matthew Wilcox]

On Thu, Feb 26, 2009 at 12:16:00AM -0500, Martin K. Petersen wrote:
> >>>>> "Matthew" == Matthew Wilcox <matthew@wil.cx> writes:
> 
> Matthew> Lowest aligned logical block address=0
> 
> Matthew> This disagrees with Martin's assertion.
> 
> Quick answer from one of my contacts.  Desktop drives will indeed ship
> with an alignment of 1(*).  The alignment is hardwired at time of
> manufacture and can't be changed.

Hm.  I'll have to poke my contacts about this drive they've given me then.
I just checked (with hdparm --Istdout) and word 209 is 0x4000 with
this drive.

> (*) I had to go back and reread the ATA spec to grok this.  READ
> CAPACITY(16) indicates the lowest naturally aligned LBA.  With LBA 63
> offset in play that would be LBA 7.
> 
> ATA, on the other hand, indicates how much LBA 0 is offset from the
> beginning of the first physical sector.  If LBA 63 is naturally aligned
> that means that LBA 0 is offset 512 bytes (physical sector 0 starts at
> LBA -1 if you will). Hence IDENTIFY DEVICE word 209 will contain 0x4001.
> 
> So you need to tweak your RC16 response a bit...

You're right.  I think I want something like:

((1 << log_per_phys) - first_sector_offset) % (1 << log_per_phys);

If you have 8 logical sectors per physical, and ATA reports 0x4001, SCSI
wants to hear 7.  The only corner case is ATA reporting 0x4000 and SCSI
wanting to hear 0, not 8, hence the % (1 << log_per_phys).

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."

Re: ATA support for 4k sector size

[H. Peter Anvin]

Martin K. Petersen wrote:
> 
> Quick answer from one of my contacts.  Desktop drives will indeed ship
> with an alignment of 1(*).  The alignment is hardwired at time of
> manufacture and can't be changed.
> 

Oh God.

This is a disaster.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

Re: ATA support for 4k sector size

[Martin K. Petersen]

>>>>> "hpa" == H Peter Anvin <hpa@zytor.com> writes:

>> Quick answer from one of my contacts.  Desktop drives will indeed
>> ship with an alignment of 1(*).  The alignment is hardwired at time
>> of manufacture and can't be changed.
>> 

hpa> Oh God.

hpa> This is a disaster.

Rationale being that modern Microsoft operating systems know how to
interpret the alignment bits.  Legacy XP will work without changes
thanks to the shifted alignment.  And Vista+ will do the right thing to
align partition 1 to what the drive reports.

Also note that Windows only aligns the first partition.  That's
something we need to be aware of when setting up dual boot systems.

-- 
Martin K. Petersen	Oracle Linux Engineering

Re: ATA support for 4k sector size

[H. Peter Anvin]

Martin K. Petersen wrote:
>>>>>> "hpa" == H Peter Anvin <hpa@zytor.com> writes:
> 
>>> Quick answer from one of my contacts.  Desktop drives will indeed
>>> ship with an alignment of 1(*).  The alignment is hardwired at time
>>> of manufacture and can't be changed.
>>>
> 
> hpa> Oh God.
> 
> hpa> This is a disaster.
> 
> Rationale being that modern Microsoft operating systems know how to
> interpret the alignment bits.  Legacy XP will work without changes
> thanks to the shifted alignment.  And Vista+ will do the right thing to
> align partition 1 to what the drive reports.
> 
> Also note that Windows only aligns the first partition.  That's
> something we need to be aware of when setting up dual boot systems.
> 

Yeah, but all of this completely breaks the disk image abstraction, 
which is a very powerful paradigm.

	-hpa

Re: ATA support for 4k sector size

[Greg Freemyer]

On Thu, Feb 26, 2009 at 5:02 PM, H. Peter Anvin <hpa@zytor.com> wrote:
> Martin K. Petersen wrote:
>>>>>>>
>>>>>>> "hpa" == H Peter Anvin <hpa@zytor.com> writes:
>>
>>>> Quick answer from one of my contacts.  Desktop drives will indeed
>>>> ship with an alignment of 1(*).  The alignment is hardwired at time
>>>> of manufacture and can't be changed.
>>>>
>>
>> hpa> Oh God.
>>
>> hpa> This is a disaster.
>>
>> Rationale being that modern Microsoft operating systems know how to
>> interpret the alignment bits.  Legacy XP will work without changes
>> thanks to the shifted alignment.  And Vista+ will do the right thing to
>> align partition 1 to what the drive reports.
>>
>> Also note that Windows only aligns the first partition.  That's
>> something we need to be aware of when setting up dual boot systems.
>>
>
> Yeah, but all of this completely breaks the disk image abstraction, which is
> a very powerful paradigm.
>
>        -hpa
>
If the reported geometry of these drives was changed to have sectors /
track be a multiple of 8, wouldn't that fix most of the issues.

ie. If the drive were to report 56 sectors per track, then a
traditional partitioning tool would start the first partition as
sector 56 and a Vista like partitioning tool would place the first
partition at sector 2048.  Both would have the same 4K sector
alignment.

If my logic is sound, anyway to get this recommendation upstream to
hardware manufacturers.  It seems like an almost trivial change for
them.

FYI: It sounds to me like partitioning tools should totally drop
efforts to align with cylinders, instead they should start asking what
the unit of atomic read/writes is at the physical layer and if any
offsets are needed to align the partition with the atomic write areas.

That would fit better for both SSD technology and for this 4K sectors
issue than trying to continue to support cylinders at all.

Thanks
Greg
-- 
Greg Freemyer
Head of EDD Tape Extraction and Processing team
Litigation Triage Solutions Specialist
http://www.linkedin.com/in/gregfreemyer
First 99 Days Litigation White Paper -
http://www.norcrossgroup.com/forms/whitepapers/99%20Days%20whitepaper.pdf

The Norcross Group
The Intersection of Evidence & Technology
http://www.norcrossgroup.com

Re: ATA support for 4k sector size

[H. Peter Anvin]

Greg Freemyer wrote:
> If the reported geometry of these drives was changed to have sectors /
> track be a multiple of 8, wouldn't that fix most of the issues.
> 
> ie. If the drive were to report 56 sectors per track, then a
> traditional partitioning tool would start the first partition as
> sector 56 and a Vista like partitioning tool would place the first
> partition at sector 2048.  Both would have the same 4K sector
> alignment.
> 
> If my logic is sound, anyway to get this recommendation upstream to
> hardware manufacturers.  It seems like an almost trivial change for
> them.
> 
> FYI: It sounds to me like partitioning tools should totally drop
> efforts to align with cylinders, instead they should start asking what
> the unit of atomic read/writes is at the physical layer and if any
> offsets are needed to align the partition with the atomic write areas.
> 
> That would fit better for both SSD technology and for this 4K sectors
> issue than trying to continue to support cylinders at all.

As long as BIOSes played along with it (which some of them may not do --
remember the geometry that matters is the one reported by the BIOS)
However, it definitely would be a major step in the right direction, as
it would let *most* systems Do The Right Thing instead of weirdly
misaligning the partitions and trying to cope with that.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

Re: ATA support for 4k sector size

[Greg Freemyer]

On Mon, Mar 16, 2009 at 12:27 PM, H. Peter Anvin <hpa@zytor.com> wrote:
> Greg Freemyer wrote:
>> If the reported geometry of these drives was changed to have sectors /
>> track be a multiple of 8, wouldn't that fix most of the issues.
>>
>> ie. If the drive were to report 56 sectors per track, then a
>> traditional partitioning tool would start the first partition as
>> sector 56 and a Vista like partitioning tool would place the first
>> partition at sector 2048.  Both would have the same 4K sector
>> alignment.
>>
>> If my logic is sound, anyway to get this recommendation upstream to
>> hardware manufacturers.  It seems like an almost trivial change for
>> them.
>>
>> FYI: It sounds to me like partitioning tools should totally drop
>> efforts to align with cylinders, instead they should start asking what
>> the unit of atomic read/writes is at the physical layer and if any
>> offsets are needed to align the partition with the atomic write areas.
>>
>> That would fit better for both SSD technology and for this 4K sectors
>> issue than trying to continue to support cylinders at all.
>
> As long as BIOSes played along with it (which some of them may not do --
> remember the geometry that matters is the one reported by the BIOS)
> However, it definitely would be a major step in the right direction, as
> it would let *most* systems Do The Right Thing instead of weirdly
> misaligning the partitions and trying to cope with that.
>
>        -hpa

I'm not intimate with the details, but I would hope most boot loaders
by now use LBA values to find the boot code, not CHS.

If so the issue becomes the partitioning tools (fdisk etc.) putting
the partitions at the right place.  Can't those tools bypass the bios
somehow and ask the drive itself what it's geometry is?

>From what I understand Vista has already made the jump and is now
ignoring CHS and instead just putting the first partition at 1 MiB
into the drive.  (sector 2048 with 512 byte sectors.)

Sounds like fdisk and friends should be updated to do the same.

A bigger issue in my mind is lots of clones, images, etc. are probably
LBA based today and simply start the first partition at sector 63.
Thus the hardware vendors will need to have drives that perform well
with partitions that start at sector 63.  The existing scheme
described may be as good as it gets for that need.

Also, how are SDD manufacturers handling this.  Their erase blocks
don't align with partitions that start at sector 63 either I assume?

Greg
-- 
Greg Freemyer
Head of EDD Tape Extraction and Processing team
Litigation Triage Solutions Specialist
http://www.linkedin.com/in/gregfreemyer
First 99 Days Litigation White Paper -
http://www.norcrossgroup.com/forms/whitepapers/99%20Days%20whitepaper.pdf

The Norcross Group
The Intersection of Evidence & Technology
http://www.norcrossgroup.com

Re: ATA support for 4k sector size

[H. Peter Anvin]

Greg Freemyer wrote:
> 
> I'm not intimate with the details, but I would hope most boot loaders
> by now use LBA values to find the boot code, not CHS.
> 

Yes, for "true" hard drives this is pretty much universal these days 
(except for MS-DOS and its ilk.)  For USB and so on some BIOSes are 
still stuck in old times.  Sigh.

> If so the issue becomes the partitioning tools (fdisk etc.) putting
> the partitions at the right place.  Can't those tools bypass the bios
> somehow and ask the drive itself what it's geometry is?

It can, but it MUST NOT do so.  The fields that are to be entered into 
the partition table are BIOS CHS values, not any other kind of CHS.

> From what I understand Vista has already made the jump and is now
> ignoring CHS and instead just putting the first partition at 1 MiB
> into the drive.  (sector 2048 with 512 byte sectors.)
> 
> Sounds like fdisk and friends should be updated to do the same.

Yes, that is way overdue.

> A bigger issue in my mind is lots of clones, images, etc. are probably
> LBA based today and simply start the first partition at sector 63.
> Thus the hardware vendors will need to have drives that perform well
> with partitions that start at sector 63.  The existing scheme
> described may be as good as it gets for that need.
> 
> Also, how are SDD manufacturers handling this.  Their erase blocks
> don't align with partitions that start at sector 63 either I assume?

Some SDD manufacturers (I don't know which ones) are actually examining 
the partition table and doing different things.  I know this because 
they are permanently bricked if one writes an invalid partition table.

Not recommended.

	-hpa

Re: ATA support for 4k sector size

[Bill Davidsen]

H. Peter Anvin wrote:
> Greg Freemyer wrote:
>>
>> I'm not intimate with the details, but I would hope most boot loaders
>> by now use LBA values to find the boot code, not CHS.
>>
> 
> Yes, for "true" hard drives this is pretty much universal these days 
> (except for MS-DOS and its ilk.)  For USB and so on some BIOSes are 
> still stuck in old times.  Sigh.
> 
>> If so the issue becomes the partitioning tools (fdisk etc.) putting
>> the partitions at the right place.  Can't those tools bypass the bios
>> somehow and ask the drive itself what it's geometry is?
> 
> It can, but it MUST NOT do so.  The fields that are to be entered into 
> the partition table are BIOS CHS values, not any other kind of CHS.
> 
I can recall playing with the disk "geometry" in the expert part of fdisk and 
not getting any particular bad effects, so I'm not sure why you MUST NOT other 
than the SSD you mentioned. However, the reason it was long ago is that aligning 
things in some possibly batter way didn't make a measurable difference in 
performance, so I went back to defaults, so I agree with your advice, it doesn't 
seem to help.

-- 
Bill Davidsen <davidsen@tmr.com>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot

Re: ATA support for 4k sector size

[James Bottomley]

On Mon, 2009-03-16 at 10:51 -0400, Greg Freemyer wrote: 
> On Thu, Feb 26, 2009 at 5:02 PM, H. Peter Anvin <hpa@zytor.com> wrote:
> > Martin K. Petersen wrote:
> >>>>>>>
> >>>>>>> "hpa" == H Peter Anvin <hpa@zytor.com> writes:
> >>
> >>>> Quick answer from one of my contacts.  Desktop drives will indeed
> >>>> ship with an alignment of 1(*).  The alignment is hardwired at time
> >>>> of manufacture and can't be changed.
> >>>>
> >>
> >> hpa> Oh God.
> >>
> >> hpa> This is a disaster.
> >>
> >> Rationale being that modern Microsoft operating systems know how to
> >> interpret the alignment bits.  Legacy XP will work without changes
> >> thanks to the shifted alignment.  And Vista+ will do the right thing to
> >> align partition 1 to what the drive reports.
> >>
> >> Also note that Windows only aligns the first partition.  That's
> >> something we need to be aware of when setting up dual boot systems.
> >>
> >
> > Yeah, but all of this completely breaks the disk image abstraction, which is
> > a very powerful paradigm.
> >
> >        -hpa
> >
> If the reported geometry of these drives was changed to have sectors /
> track be a multiple of 8, wouldn't that fix most of the issues.
> 
> ie. If the drive were to report 56 sectors per track, then a
> traditional partitioning tool would start the first partition as
> sector 56 and a Vista like partitioning tool would place the first
> partition at sector 2048.  Both would have the same 4K sector
> alignment.
> 
> If my logic is sound, anyway to get this recommendation upstream to
> hardware manufacturers.  It seems like an almost trivial change for
> them.

This is Ted Ts'o's proposed fix for the problem as well ... we do the
C/H/S translation in scsicam.c and it's then stored in the DOS partition
label.  The only problems are that changing this on the fly might be
problematic for things that believe scsicam_bios_param without first
checking the DOS label (because they'll then be mismatched).  And also,
if the vendors use their power to offset the first 4k block, we'll be
mismatched again.  Plus, once the values are written in the label we
can't update them.

> FYI: It sounds to me like partitioning tools should totally drop
> efforts to align with cylinders, instead they should start asking what
> the unit of atomic read/writes is at the physical layer and if any
> offsets are needed to align the partition with the atomic write areas.
> 
> That would fit better for both SSD technology and for this 4K sectors
> issue than trying to continue to support cylinders at all.

The DOS label is the problematic one ... all the rest have (mostly) more
sensible schemes.  The problem is that the DOS label is the most
prevalent one.

James