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

To: Michael Monnerie <michael.monnerie@xxxxxxxxxxxxxxxxxxx>
Subject: Re: 4K drives, sectsz=512, bsize=4096
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Tue, 31 Aug 2010 17:15:29 -0500
Cc: xfs@xxxxxxxxxxx
In-reply-to: <201009010007.23899@xxxxxx>
References: <201008300956.21264@xxxxxx> <201008312301.38103@xxxxxx> <4C7D7141.4070406@xxxxxxxxxxx> <201009010007.23899@xxxxxx>
User-agent: Thunderbird 2.0.0.24 (Macintosh/20100228)
Michael Monnerie wrote:
> 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?

the log can do things on sector size boundaries.
 
> 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?

I don't think so ...

-Eric

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