Re: [Bug-ddrescue] SMART, reallocation, and retries

[Antonio Diaz Diaz]

Dear Franc,

Franc Zabkar wrote:
> AIUI, modern hard drives fail with "weak heads". This means that data 
> recovery software should avoid hammering at bad sectors for two reasons. 

AFAIK, ddrescue uses the most sophisticated algorithm in any recovery 
software in order to avoid hammering at bad sectors.


> May I suggest that ddrescue disable SMART by default, if it does not 
> already do so. Also I believe that there may be ATA commands that allow 
> retries to be disabled at the drive level, at least in earlier versions 
> of the standard.

Changing drive parameters (for example, disabling retries at drive 
level) is a complex and unportable task. There exist tools for this task 
(hdparm[1], smartmontools[2]) and it would be dangerous to try to 
automate the function of these tools inside ddrescue.

The Wikipedia says this about hdparm[3]:
"hdparm has a more serious drawback: it can crash a computer and make 
data on its disk inaccessible if certain parameters are misused. Out of 
approximately sixty-seven parameters, several are dangerous and could 
result in "massive filesystem corruption" when used indiscriminately."

And the same can be said about ddrescue or any other data recovery tool.

[1] http://man7.org/linux/man-pages/man8/hdparm.8.html
[2] http://smartmontools.sourceforge.net/man/smartctl.8.html
[3] http://en.wikipedia.org/wiki/Hdparm

I plan to add some references to these tools to the ddrescue manual. 
Examples of successful rescue cases using them are welcome.


Best regards,
Antonio.