[Bug-ddrescue] http://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html

[John Summerfield]

I have need of this program, and it's not going well. I have a seagate 
drive that is terminally ill. It seems to me its problem is on the 
circuit board rather than amongst the platters. It's in the fridge while 
I do some research.

First thing is that the above page needs revision. Recent drives have 4K 
sectors. See
http://www.seagate.com/tech-insights/advanced-format-4k-sector-hard-drives-master-ti/
and other places. Hopefully, you can discover the native sector size 
programatically.

On this particular drive, things get a little bizarre. The kernel 
reported the drive capacity changed(!!) to zero, and ddrescue, going 
backwards at the time, concluded it had finished and left my image 
starting with (quite a) few gigabytes of zeros. I suspect the log isn't 
useful.

First, (after trying with dd), I went forwards, and when it stopped and 
I, not realising just how oddly the drive was behaving, restarted 
ddrescue in reverse. That destroyed the log file, it contained numbers 
way outside the drive's capacity.

The dodgy disk drive's capacity is 500 Gbytes, I don't have a lot of 
space for backing up images...

Since reverse gear doesn't seem to work with this drive, my next attempt 
will be to start again from the beginning. When it fails, the drive 
returns to the cool place for a while, and then I will simply rerun 
using the existing files.

I will, of course, override the blocksize. While I am looking at it, I 
suggest the default cluster-size be a function of available RAM. Using a 
64K buffer might have been reasonable on RHL 7.x or Debian Potato, but 
with 8 Gbytes of RAM I can spare a little more.

The version of ddrescue I tried is that shipped on the systemrescuecd 
that I downloaded withing the past week.

I am creating my own rescue image based on Fedora 18, there are aspects 
of the systemrescuecd which I don't like. Using a read-write image on a 
usb disk, I can customise whenever I like, including on the system I'm 
trying to rescue.

It's time I tried again.
--
John