linux-kernel - Re: ATA 4 KiB sector issues.

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Message-id: <4B97C6A5.4010209@tvk.rwth-aachen.de>
Date:	Wed, 10 Mar 2010 17:19:49 +0100
From:	Damian Lukowski <damian@....rwth-aachen.de>
To:	"linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>
Cc:	Jeff Garzik <jeff@...zik.org>, Matthew Wilcox <matthew@....cx>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	James Bottomley <James.Bottomley@...e.de>,
	Tejun Heo <tj@...nel.org>, lkml <linux-kernel@...r.kernel.org>,
	Daniel Taylor <Daniel.Taylor@....com>,
	Mark Lord <kernel@...savvy.com>, tytso@....edu,
	"H. Peter Anvin" <hpa@...or.com>, hirofumi@...l.parknet.co.jp,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>, irtiger@...il.com,
	aschnell@...e.de, knikanth@...e.de, jdelvare@...e.de
Subject: Re: ATA 4 KiB sector issues.

> S-2. The proper solution.
> 
>   Correct alignments for all partitions can't be achieved by the
>   firmware alone.  The system utilities should be informed about the
>   alignment requirements and align partitions accordingly.
> 
>   The above firmware workaround complicates the situation because the
>   two different configurations require different offsets to achieve
>   the correct alignments.  ATA/ATAPI-8 specifies a way for a drive to
>   export the physical and logical sector sizes and the LBA offset
>   which is aligned to the physical sectors.
> 
>   In Linux, these parameters are exported via the following sysfs
>   nodes.
> 
>     physical sector size	: /sys/block/sdX/queue/physical_block_size
>     logical sector size		: /sys/block/sdX/queue/logical_block_size
>     alignment offset		: /sys/block/sdX/alignment_offset
> 
>   Let the physical sector size be PSS, logical sector size LSS and
>   alignment offset AOFF.  The system software should place partitions
>   such that the starting LBAs of all partitions are aligned on
> 
>     (n * PSS + AOFF) / LSS
> 
>   For 4 KiB physical sector offset-by-one drives, PSS is 4096, LSS 512
>   and AOFF 3584 and with n of 7 the above becomes,
> 
>     (7 * 4096 + 3584) / 512 == 63
> 
>   making sector 63 an aligned LBA where the first partition can be
>   put, but without the offset-by-one mapping, AOFF is zero and LBA 63
>   is not aligned.
> 
>   With the above new alignment requirement in place, it becomes
>   difficult to honor the legacy one - first partition on sector 63 and
>   all other partitions on cylinder boundary (255 * 63 sectors) - as
>   the two alignment requirements contradict each other.  This might be
>   worked around by adjusting how LBA and CHS addresses are mapped but
>   the disk geometry parameters are hard coded everywhere and there is
>   no reliable way to communicate custom geometry parameters.

Hello,
I have practically no knowledge of Linux' block device drivers,
but is this really a partitioning issue? I think the problem is
with the filesystems when clustering multiple blocks without
knowledge of the sector alignment and sector size of the underlying
block device. Maybe it is a better solution to adapt the filesystem
buffer routine which reads/writes data from/to the block device?

Best regards
 Damian
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