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Re: [Bug-ddrescue] Request for an Especific Clone Direction Option

From: Antonio Diaz Diaz
Subject: Re: [Bug-ddrescue] Request for an Especific Clone Direction Option
Date: Tue, 13 May 2014 17:45:57 +0200
User-agent: Mozilla/5.0 (X11; U; Linux i586; en-US; rv:1.7.11) Gecko/20050905

Hello William,

William wrote:
At first, I'd like to thank all the people involved in this great project, specially Mr. Antonio Diaz.

You are welcome.

I have realized that Ddrescue v1.18 automatically changes its clone direction from "forward" to "backward" when it finds some bad sector (even using --no-retry parameter). I think this happen due the new algorithm.

Ddrescue 1.18-pre9 and later versions alternate direction of passes during the copying phase, but only after reaching the end of the rescue domain in the forward direction. If you do not want ddrescue to reach a given area, just limit the rescue domain. For example, the command:

  ddrescue -s 1TB /dev/sda /dev/sdb logfile

will never try to read any data beyond the 1 TB position. It will first read forwards up to 1 TB, then backwards from 1 TB down.

This automated behavior can be very bad in cases which is needed to have more precise control over clone process (such as the clone direction), when handling scratched disks, per example. In such cases, it's quite important to keep the heads away from scratched areas to prevent permanent damages.

Just setting the copy direction does not prevent the heads from eventually reaching the scratched area. You also need to limit the rescue domain as explained above.

Is there a way to force Ddrescue to run in only one especific direction (at least in --no-retry mode)? Per example, "ddrescue --forward --force /dev/sda /dev/sdb" to run only in forward direction.

Currently not, but it can be added if needed.

Best regards,

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