Re: How can i read really 512 byte?

[Janos Haar]

----- Original Message ----- 
From: "Andrey Borzenkov" <arvidjaar@xxxxxxx>
To: "Milton Miller" <miltonm@xxxxxxx>; <janos.haar@xxxxxxxxxxxx>; "Linux 
Kernel Mailing List" <linux-kernel@xxxxxxxxxxxxxxx>
Sent: Wednesday, October 01, 2008 2:36 PM
Subject: Re: How can i read really 512 byte?


> Milton Miller wrote:
>
> > On Oct 1, 2008, at 5:23 AM, Janos Haar wrote:
> >
> > > > 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?
> >
> > dd_rescue ... there is a call to open, add O_DIRECT to the second
> > argument and recompile.  If it says unknown identifier, just copy the
> > #define from the kernel header into the dd_rescue source.
>
> C'mon, really.
>
> {pts/0}% dd_rescue -h
>
> dd_rescue Version 1.14, garloff@xxxxxxx, GNU GPL
> [...]
>         -b softbs  block size for copy operation (def=65536),
>         -B hardbs  fallback block size in case of errs (def=512),
> [...]
>         -d/D       use O_DIRECT for input/output (def=no),

YES! 8-)
It works! :-)

Thank you wery much for you, and Milton!

Thanks
Janos Haar

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