DDRESCUE examples in the GNU website + 1 kind question

[Roberto Gini]

Dear Antonio, this is Roberto from Verona, Italia une ddrescue user

thank you so much for your work with ddrescue.

I'd like to suggest an additional example in this section
http://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html#Examples

if you read over the internet, ddrescue is, together with forensic, mostly suggested for very bad drives (lot of bad sectors and drives becoming unstable)

why don't you add a specific example and sequence for the case "cloning a drive with a lot of bad sectors" ?

Additionally, I'd like to ask you why don't to implement a user definable skip ahead size amount and read backward , in case of bad sectors encountering. I've read the algorithm, but this is a little different and would give the user a better feeling of what is going on with the drive.
As example, starting to clone a 500GB bad drive, I notice that after 20GB of nice cloning, they rises a lot of errors. In my idea I would stop the cloning and choose to add a --skip-ahead-icoe=1M (icoe=in case of error). The goal is to understand if one megabyte forward, the situation is better.
If the situation is better, I would expect ddrescue to start reading backward this 1MB portion until the first error happen, at this point, ddrescue will return to the initial skip ahead point to continue the disk cloning in forward direction.
To end up and finish with my request (any explanation about this request to be a non sense will be appreciated and welcome) I would say that if 1MB falls again in bad areas, I would skip 5MB or 10MB or 50MB.

Thank you for any answer, about the example request and also regarding the feature.

Roberto

P.S. there are some drives that are recognized nice by the BIOS, they do not make bad noises but as soon linux or windows starts effectively to boot, such drives (either if connected on secondary channels) hangs the windows boot. It would be nice to have a ddrescue like tool interfacing directly with the ATA interface. Do you know something similar out there? Have you ever thought about this?

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[Reon Toerien]

As far as I'm aware Antonio is looking into the skip ahead size option, there has been a few back & forward mails about such a feature in the last two weaks so maybe read the other topics in this mailing list.

I asked about a reverse read a long time ago but I cannot remember the replies.

Cheers

On 5 October 2011 22:02, Roberto Gini <gini.robert@...> wrote:

Dear Antonio, this is Roberto from Verona, Italia une ddrescue user

thank you so much for your work with ddrescue.

I'd like to suggest an additional example in this section
http://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html#Examples

if you read over the internet, ddrescue is, together with forensic, mostly suggested for very bad drives (lot of bad sectors and drives becoming unstable)

why don't you add a specific example and sequence for the case "cloning a drive with a lot of bad sectors" ?

Additionally, I'd like to ask you why don't to implement a user definable skip ahead size amount and read backward , in case of bad sectors encountering. I've read the algorithm, but this is a little different and would give the user a better feeling of what is going on with the drive.
As example, starting to clone a 500GB bad drive, I notice that after 20GB of nice cloning, they rises a lot of errors. In my idea I would stop the cloning and choose to add a --skip-ahead-icoe=1M (icoe=in case of error). The goal is to understand if one megabyte forward, the situation is better.
If the situation is better, I would expect ddrescue to start reading backward this 1MB portion until the first error happen, at this point, ddrescue will return to the initial skip ahead point to continue the disk cloning in forward direction.
To end up and finish with my request (any explanation about this request to be a non sense will be appreciated and welcome) I would say that if 1MB falls again in bad areas, I would skip 5MB or 10MB or 50MB.

Thank you for any answer, about the example request and also regarding the feature.

Roberto

P.S. there are some drives that are recognized nice by the BIOS, they do not make bad noises but as soon linux or windows starts effectively to boot, such drives (either if connected on secondary channels) hangs the windows boot. It would be nice to have a ddrescue like tool interfacing directly with the ATA interface. Do you know something similar out there? Have you ever thought about this?

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Kind Regards
Reon Toerien
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[Antonio Diaz Diaz]

Hello Reon,

Reon Toerien wrote:
> As far as I'm aware Antonio is looking into the skip ahead size option,
> there has been a few back & forward mails about such a feature in the last
> two weaks so maybe read the other topics in this mailing list.

I have just announced[1] 1.15-pre2 which includes the new option "-a,
--min-read-rate" for skipping over slow areas. Currently ddrescue uses
the same jumping algorithm for slow areas and damaged areas. Lets see
how well it works before adding yet another option.
[1]https://lists.gnu.org/archive/html/bug-ddrescue/2011-10/msg00004.html


> I asked about a reverse read a long time ago but I cannot remember the
> replies.

Reverse read is implemented since version 1.14-pre2 (2010-11-27).
https://lists.gnu.org/archive/html/bug-ddrescue/2010-11/msg00010.html


Best regards,
Antonio.

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[Antonio Diaz Diaz]

Hello Roberto,

Roberto Gini wrote:
> thank you so much for your work with ddrescue.

You are welcome. :-)


> why don't you add a specific example and sequence for the case "cloning a
> drive with a lot of bad sectors" ?

Ddrescue can manage any number of bad sectors without special options.
Of course an experienced user can shorten rescue time, but it depends on
the drive's behaviour and I don't think any single example can cover all
cases.

BTW, have you looked at the example shown here
http://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html#Algorithm


> Additionally, I'd like to ask you why don't to implement a user definable *skip
> ahead size amount* *and read backward* , in case of bad sectors
> encountering.

Ddrescue already skips ahead an exponentially growing amount depending
on rate and error history. It totaly skips an unreadable 1.44 MB floppy
in 8 seconds. I don't think the skip value needs to be made any larger.

Reading backwards is much slower than reading forwards. So jumps should
not be too large, and all trimming is best done in a second pass.


> P.S. there are some drives that are recognized nice by the BIOS, they do not
> make bad noises but as soon linux or windows starts effectively to boot,
> such drives (either if connected on secondary channels) hangs the windows
> boot. It would be nice to have a ddrescue like tool interfacing directly
> with the ATA interface. Do you know something similar out there? Have you
> ever thought about this?

As far as I know, ddrescue doesn't run on windows so, as long as the
drive does not hang the linux boot, this is not a problem. About using
interfaces directly, I have already decided not to do it.


Best regards,
Antonio.

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