Message-ID: <4422C316.5070305@cfl.rr.com>
Date: Thu, 23 Mar 2006 10:47:34 -0500
From: Phillip Susi <psusi@cfl.rr.com>
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To: Yogesh Pahilwan <pahilwan.yogesh@spsoftindia.com>
CC: linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org
Subject: Re: raw I/O support for Fedora Core 4
References: <WM57DB3DF98115400697C908A54A80DEE9@spsoftindia.com>
In-Reply-To: <WM57DB3DF98115400697C908A54A80DEE9@spsoftindia.com>
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The raw device driver is obsolete because it has been superseded by the 
O_DIRECT open flag.  If you want to have dd perform unbuffered IO then 
pass the iflag=direct option for input, or oflag=direct option for 
output, and it will use O_DIRECT to bypass the buffer cache.

This of course assumes that you mean "bypass the buffer cache" when you 
say "raw io".

Yogesh Pahilwan wrote:
> Hi All,
> 
> I want to do raw I/O on MD RAID and LVM for fedora core 4(kernel 2.6.15.6).
> 
> After doing googling I came to know that "raw" command does the raw
> operation by linking 
> MD device and LVM volume to the raw device as 
> 
> # raw /dev/raw/raw1 /dev/md0.
> 
> But when I search on this I came to know that there is no raw (/dev/rawctl)
> device support available with 2.6 kernel.
> I have also tried recompile the kernel sources with raw device support it is
> not getting compiled as it is obsolete in 2.6. 
> If I want to include raw device support in my kernel what should I will have
> to do, so that I 
> Will be able to do raw I/O on MD device and LVM volumes.
> 
> Thanks and Regards,
> Yogesh
> 

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