linux-kernel - Re: How can i read really 512 byte?

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Message-ID: <409101c923af$c8092020$0400a8c0@dcccs>
Date:	Wed, 1 Oct 2008 12:23:32 +0200
From:	"Janos Haar" <janos.haar@...center.hu>
To:	"Milton Miller" <miltonm@....com>
Cc:	<linux-kernel@...r.kernel.org>
Subject: Re: How can i read really 512 byte?


----- Original Message ----- 
From: "Milton Miller" <miltonm@....com>
To: "Janos Haar" <janos.haar@...center.hu>
Cc: <linux-kernel@...r.kernel.org>
Sent: Tuesday, September 30, 2008 4:50 PM
Subject: How can i read really 512 byte?


> On Tue, 30 Sep 2008 at 08:29:15 -0400 (EDT), Janos Haar wrote:
>> Now i am working on recover some data from one defective drive.  I
>> am using dd_rescue, and dd, but both ready only 4K, i think, because
>> the kernel's block size is 4K.
>> 
>> I have tried to google for the solution, but only found this trick:
>> 
>> losetup /dev/loop0 /dev/hdc
>> blockdev --setbsz 512 /dev/hdc
>> 
>> and after this set, trying to read the hdc...
>> 
>> It looks like working on the first look, but not really. :-( The
>> 512 size bad sectors still have 4K sizes, but the reading attempt
>> takes more (8x ?) longer.
>> 
>> Somebody can help me to set the reading block size to 512 byte?
> 
> You need to add O_DIRECT to the open call in the flags parameter
> (the second argument).   (My brother tested this a year or so ago,
> and it worked for him).
> 
> milton

Hello,

Thank you for the information.
Can you help me a little bit more?
Where need to add this parameter?
In the kernel, in the blocked's source, or in the dd_rescue's source?

Thanks,
Janos Haar
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