How can i read really 512 byte?

How can i read really 512 byte?

[Janos Haar]

Hello list,

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?

Thanks a lot,
Janos Haar 

How can i read really 512 byte?

[Milton Miller]

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

Re: How can i read really 512 byte?

[Janos Haar]

----- Original Message ----- 
From: "Milton Miller" <miltonm@bga.com>
To: "Janos Haar" <janos.haar@netcenter.hu>
Cc: <linux-kernel@vger.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

Re: How can i read really 512 byte?

[Milton Miller]

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.

milton

Re: How can i read really 512 byte?

[Andrey Borzenkov]

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@suse.de, 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),

Re: How can i read really 512 byte?

[Janos Haar]

----- Original Message ----- 
From: "Andrey Borzenkov" <arvidjaar@mail.ru>
To: "Milton Miller" <miltonm@bga.com>; <janos.haar@netcenter.hu>; "Linux 
Kernel Mailing List" <linux-kernel@vger.kernel.org>
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@suse.de, 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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