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Re: NOW: o_direct -- WAS: Re: WARNING in xfs_lwr.c, xfs_write()

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>, Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>
Subject: Re: NOW: o_direct -- WAS: Re: WARNING in xfs_lwr.c, xfs_write()
From: Stewart Smith <stewart@xxxxxxxxxxxxxxxx>
Date: Thu, 27 May 2010 23:58:55 +1000
Cc: xfs@xxxxxxxxxxx
In-reply-to: <20100527114736.GA13112@xxxxxxxxxxxxx>
References: <20100523002023.41f5a5c8@xxxxxxxxxxxxxxxxxxxxxxx> <20100523101856.GL2150@dastard> <20100523092344.0fcaab42@xxxxxxxxxxxxxxxxxxxxxxx> <4BF9FCA8.8090906@xxxxxxxxxxxxxxxxx> <20100524143428.6f3a117c@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx> <20100526070620.GT2150@dastard> <4BFD3926.6040208@xxxxxxxxxxxxxxxxx> <20100527114736.GA13112@xxxxxxxxxxxxx>
User-agent: Notmuch/0.3.1-17-gc50524e (http://notmuchmail.org) Emacs/23.1.1 (x86_64-pc-linux-gnu)
On Thu, 27 May 2010 07:47:37 -0400, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
> O_DIRECT is not a Posix standard and not very portable.  It originated
> on IRIX, and Linux inherited it during the 2.4 kernel series days.
> These days FreeBSD/NetBSD and AIX support it as well, but for example
> Solaris, HP-UX and OpenBSD don't, nevermind Windows or Mac OS.

There is O_DIRECT type functionality available on Windows, with similar
restrictions for aligned IO too. You have to use the Win32 APIs to do it
though, the POSIX ones won't get you it (or more than 2048 files open at
once).

In practice we've only ever found Solaris (other than linux) to be
reliable with O_DIRECT (at least on UFS... ZFS is... well... I wouldn't
run a database server on it yet).

-- 
Stewart Smith

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