From: Christoph Hellwig <hch@infradead.org>
To: Eric Sandeen <sandeen@redhat.com>
Cc: xfs-oss <xfs@oss.sgi.com>
Subject: Re: [PATCH RFC] xfs: set block device logical sector size on xfs_buftarg
Date: Wed, 13 Nov 2013 10:56:45 -0800 [thread overview]
Message-ID: <20131113185645.GA20869@infradead.org> (raw)
In-Reply-To: <5283C41D.7070503@redhat.com>
On Wed, Nov 13, 2013 at 12:25:33PM -0600, Eric Sandeen wrote:
> Pure RFC; this might be crazy. Here's the problem I'm trying to solve:
>
> Today, mkfs.xfs will select a 4k sector size for a 4k physical / 512 logical
> drive. (that change was done by me). The thought was that it'd be an
> efficiency gain to not make the drive do the (possible) RMW cycles on
> 512-byte log IO, primarily.
>
> However, now this restricts all DIO to 4k alignment, not the otherwise-
> possible 512.
>
> This came up when qemu-kvm, in cache=none mode, tries to boot off an
> image hosted on such a filesystem, and its bios wants to do a 512 byte
> direct IO read off the disk - it fails.
>
> But I'm wondering - the buftarg's bt_sshift and bt_smask are only used
> in a few places.
No need to mess with kernel code IFF we want to change that, just keep
the sector size at 512 bytes and set a log stripe unit at mkfs time.
I have to admit that I'm not really sure if that's what we really want,
through. A drive that has a larger physical block size will need
read-modify-write cycles internally, which we try to avoid.
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next prev parent reply other threads:[~2013-11-13 18:56 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-11-13 18:25 [PATCH RFC] xfs: set block device logical sector size on xfs_buftarg Eric Sandeen
2013-11-13 18:56 ` Christoph Hellwig [this message]
2013-11-13 19:08 ` Eric Sandeen
2013-11-13 21:26 ` Dave Chinner
2013-11-13 21:32 ` Eric Sandeen
2013-11-13 22:10 ` Dave Chinner
2013-11-13 22:18 ` Eric Sandeen
2013-11-14 0:34 ` Dave Chinner
2013-11-14 13:37 ` Christoph Hellwig
2013-11-14 14:56 ` Eric Sandeen
2013-11-14 21:01 ` Dave Chinner
2013-11-22 14:13 ` Ric Wheeler
2013-11-22 14:20 ` Christoph Hellwig
2013-11-22 14:26 ` Ric Wheeler
2013-11-22 14:57 ` Eric Sandeen
2013-11-14 0:35 ` Eric Sandeen
2013-11-14 6:49 ` Dave Chinner
2013-11-14 13:09 ` Ric Wheeler
2013-11-14 15:03 ` Eric Sandeen
2013-11-14 15:18 ` Eric Sandeen
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