From: Christoph Hellwig <hch@infradead.org>
To: Michael Monnerie <michael.monnerie@is.it-management.at>
Cc: xfs@oss.sgi.com
Subject: Re: 4K drives, sectsz=512, bsize=4096
Date: Wed, 1 Sep 2010 06:24:12 -0400 [thread overview]
Message-ID: <20100901102412.GF31648@infradead.org> (raw)
In-Reply-To: <201008300956.21264@zmi.at>
On Mon, Aug 30, 2010 at 09:56:16AM +0200, Michael Monnerie wrote:
> I have 2x 2TB 4K sector drives, joined with LVM to RAID-0. On top of
> that, I created an XFS, but that has sectsz=512.
>
> Will there be any real difference if I re-format with sectsz=4096?
> AFAIK, XFS will do I/O based on block size, so the sector size doesn't
> do any harm. Is that correct?
As nathan mentioned XFS issues log I/O based on the sector size, and
we do allow direct I/O down to the sector size. That's two reasons
why or why you don't want a 4096 byte sector size. Depending on the rmv
implementation of the drive log I/O might be really slow if you set the
512 byte sector size. On the other hand there's lots of applications
that have the 512 byte alignment for direct I/O hardcoded, which will
break if you have a larger sector size. That's one of the fun things
4k sector size disks will bring up, especially the real 4k SAS disks
that do not accept any I/O smaller than that.
> A question for LVM: Is there anything I need to tell to LVM to let it
> know that those are 4K sector drives and I/O should be aligned to that?
> Drives are reported as 512b sectors, but really are 4K. There seems to
> be no way to instruct the kernel to see those drives as 4K drives.
If you have a recent enough LVM all metdata is aligned on 1MB boundaries
which will do just fine.
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prev parent reply other threads:[~2010-09-01 10:23 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-08-30 7:56 4K drives, sectsz=512, bsize=4096 Michael Monnerie
2010-08-31 21:01 ` Michael Monnerie
2010-08-31 21:16 ` Eric Sandeen
2010-08-31 22:07 ` Michael Monnerie
2010-08-31 22:15 ` Eric Sandeen
2010-08-31 23:12 ` Michael Monnerie
2010-08-31 22:34 ` Nathan Scott
2010-09-01 5:35 ` Gim Leong Chin
2010-09-01 5:59 ` Nathan Scott
2010-09-01 7:38 ` Michael Monnerie
2010-09-01 10:13 ` Christoph Hellwig
2010-09-01 10:24 ` Christoph Hellwig [this message]
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