Re: [Bug-ddrescue] ddrescue on BSD vs Linux

[Antonio Diaz Diaz]

Hello,

luminair wrote:
> http://en.wikipedia.org/wiki/Ddrescue#Recovery-oriented_variants_of_dd
>
> It says "Linux lacks "raw" disk devices like *BSD has, which makes it
> less desirable for low-level data recovery," is this true, or just
> FUD?  Should I use FreeBSD when I try to recover my disk?

I guess it is FUD. For example see 
http://en.wikipedia.org/wiki/Raw_device where it says:
"On Linux raw devices are deprecated and scheduled for removal, because 
the O_DIRECT flag can be used instead."

Ddrescue can use O_DIRECT (option -d), but be aware that "Using direct 
disc access, or reading from a raw device, may be slower than normal 
cached reading for hard discs (but faster for floppies). In this case 
you may want to make a first pass using normal cached reads, and use 
direct disc access, or a raw device, only to recover the good sectors 
inside the failed blocks."


> Also, there is a recommended procedure there, of ddrescue -n and then
> ddrescue -r 1 afterwards. Is that your recommendation? Otherwise what
> is the good of it. You can't trust wikipedia unless the expert wrote
> it.

The advantage of using -n, then -r1 (or nothing), is that you can use 
different options in each case. For example larger cluster size in first 
try for maximum speed, then direct disc access in second try to maximize 
the amount of data recovered.


Regards,
Antonio.