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Date: Fri, 25 Dec 2009 12:30:57 -0500
From: Gary Palmer <gpalmer@freebsd.org>
To: Alexander Motin <mav@FreeBSD.org>
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Cc: FreeBSD-Current <freebsd-current@freebsd.org>, freebsd-arch@freebsd.org
Subject: Re: File system blocks alignment
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On Fri, Dec 25, 2009 at 12:58:07PM +0200, Alexander Motin wrote:
> Hi.
> 
> Recently WD released first series of ATA disks with increased physical
> sector size. It makes writes not matching with 4K blocks inefficient
> there. So I propose to get back to the question of optimal FS block
> alignment. This topic is also important for most of RAIDs having striped
> nature, such as RAID0/3/5/... and flash drives with simple controller
> (such as MMC/SD cards).

This is also a critical issue on certain SAN system.  NetApp, I suspect
as a result of them layering a virtual LUN ontop of another filesystem
(WAFL), is very sensitive to filesystem alignment on the LUN.  If the
I/Os to the LUN are not 4k aligned, performance suffers a serious hit.
I'm not sure what other SAN vendors suffer similar alignment restrictions.

Regards,

Gary