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Re: 4K drives, sectsz=512, bsize=4096

To: xfs@xxxxxxxxxxx
Subject: Re: 4K drives, sectsz=512, bsize=4096
From: Michael Monnerie <michael.monnerie@xxxxxxxxxxxxxxxxxxx>
Date: Wed, 1 Sep 2010 00:07:20 +0200
In-reply-to: <4C7D7141.4070406@xxxxxxxxxxx>
Organization: it-management http://it-management.at
References: <201008300956.21264@xxxxxx> <201008312301.38103@xxxxxx> <4C7D7141.4070406@xxxxxxxxxxx>
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On Dienstag, 31. August 2010 Eric Sandeen wrote:
> Just be sure your first sector of your top-level block device
> is 4k aligned, and then yes you'll want to set sector size to 4k
> so that xfs will do all log IO in 4k blocks as well.

I can only hope LVM does it right, I have no idea how it aligns.
 
> If you do it right (and especially vs. if you do it wrong) it should
> be a bit faster if all IOs are 4k aligned on the disk.
 
And that's what's interesting me: why? Won't XFS do all I/Os at minimum 
for a given block size? Or is it possible XFS does write only a single 
sector? I'd expect the smallest I/O size to be the block size, but it 
seems I'm wrong?

I guess there's no way to "convert" an existing XFS with 
sectsz=512,bsize=4096 to sectsz=4096,bsize=4096? Maybe that's only a 
flag that can be changed?


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Michael Monnerie, Ing. BSc

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