Re: [Bug-ddrescue] ddrescue - resume backup with a little offset

[Marian Csontos]

On 08/30/2011 10:28 PM, Seagatevictum wrote:
> Now I have two problems,

Heh, quite common thing solving one problem uncovers at least two 
others. I am almost sure that's a quote and if it was not it is now. ;-)

I hope doubling problem count will not continue...

> first the backup resumes at 3308 mg, and not at 3155
> =( mb got something to do with the logs.

Try to search MB and MiB.
Simply MiB are "binary" megabytes - thats twenty of twos multiplied = 
1,048,576.
MB are just six of tens multiplied = 1,000,000.

Then you should simply continue at 3155000000 (that's 3,155,000,000)

> And second how do I resume the copying? because when I try
>
> address@hidden:~# ddrescue  /dev/sdb6 /dev/sda3
> /media/sda4/skippp.logddrescue: Output file exists and is not a regular
> file.
> ddrescue: Use `--force' if you really want to overwrite it, but be
> ddrescue: aware that all existing data in output file will be lost.
> Try `ddrescue --help' for more information.
> address@hidden:~#
>
> and I can only resume with -f, does that delete my existing backup data?

-f protects disk partitions from accidental overwriting. Overwriting a 
single file does not do that much damage (depends) but overwriting a 
wrong partition is much more serious and non-recoverable[1] mistake 
likely blowing away all the files on the device.

[1] at least not with tools available to mere mortals. More here : 
http://en.wikipedia.org/wiki/Data_remanence

Whether it overwrites previously rescued data depends if you used 
ddrescue before with the same logfile. I believe it will not but better 
to try it out first.

-- Martian

> Marian Csontos-3 wrote:
> > On 08/30/2011 12:45 PM, Seagatevictum wrote:
> > > Hi!
> > > I ran into serious trouble. My Seagate drive with all my documents got
> > > corrupted. There’r about 10 bad blocks on the drive but each time the
> > > system
> > > tries to read from a broken sector the drive sets itself into busy mode
> > > and
> > > stops responding. Ddrescue is my best option because it can RESUME the
> > > image
> > > backup… but! For ex. I have a bad block at 3145 mg, and I want the backup
> > > to
> > > resume at 3155. I can do this using the log where the resume position is
> > > set. But how? I can’t really understand the 0x00000000 format either how
> > > does that correspond to the actual position? How can I add a “next
> > > sector”
> > > into the resume?
> > >
> > > Please help!
> >
> > Hi, I think -i option is what you need:
> >
> >   >  `-i pos'
> >   >`--input-position=pos'
> >   >     Starting position in input file, in bytes. Defaults to 0. In fill
> >   >     mode it refers to the original input file. See the chapter Fill
> >   >     Mode (see Fill Mode) for details.
> >
> > 3145 mg? Supposing that's 3145 MiB and you want to continue at 3155 MiB,
> > that's 3155 * 2**20 = 3308257280 (you can use python to calculate these)
> >
> >     ddrescue -i 3308257280 INDEV OUTDEV_OR_FILE LOGFILE
> >
> > Or in bash:
> >
> >     ddrescue -i $((3155 * 2**20)) INDEV OUTDEV_OR_FILE LOGFILE
> >
> > You will also want to use same LOGFILE to be able to resume if it locks
> > again.
> >
> > Also when it locks try the next megabyte, but on next pass try resuming
> > 3154 + 1/2 MiB, then + 1/4 MiB, and so on to get as much data as you can.
> >
> > -- Martian
> >
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