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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: Nathan Scott <nathans@xxxxxxxxxx>
Date: Wed, 1 Sep 2010 08:34:28 +1000 (EST)
Cc: xfs@xxxxxxxxxxx
In-reply-to: <201009010007.23899@xxxxxx>
----- "Michael Monnerie" <michael.monnerie@xxxxxxxxxxxxxxxxxxx> wrote:

> On Dienstag, 31. August 2010 Eric Sandeen wrote:
> > 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?

Log I/O and direct writes are sector sized & aligned.

> 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?

There's no way (other than dump, mkfs & restore), the filesystem is laid
out differently (most data structures, like superblocks and other metadata
become 4K aligned).

cheers.

-- 
Nathan

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