Re: [Bug-ddrescue] GNU ddrescue HELP

[Florian Sedivy]

Hello Kevin!

Obviously you are doing this on a Mac. This and the actual command line you 
used would have been important details to share when asking for help. 

From what I can deduce, you are using -c 4096 (or probably -c 4Ki). In my 
testing values bigger than 256 sectors of 512 bytes did not improve speed any 
further. The only drawback of such a big value however are less frequent 
updates to ddrescue's UI, so while -c 256 would be the optimal value, yours 
probably did no harm. 

You can speed up the transfer a lot by using the raw character device instead 
of the block device. So in your case that would be /dev/rdisk3s3 instead of 
/dev/disk3s3 IF the device did not change - always check the device name before 
you start ddrescue! Still you will need A LOT of patience if the drive has real 
problems and it certainly looks like it has. Let ddrescue do it's thing. 

There is no use in trying to write a partially rescued image to another 
partition. Even the last rescued byte could make all the difference to the 
validity of the enclosed filesystem. So just wait until you think you have 
everything the damaged drive is ever going to give you, before proceeding to 
the next step.

I seriously hope /Users/kevin/Desktop/MPA/recovery.log wasn't the original log 
file you used for the recovery? If it was, then you destroyed it by using it 
for restoring the image and will have to create a new one. You could either 
start over from zero or find a good backup of your log file (Time Machine?) or 
create a new log file from Rescue.dmg with ddrescue's Generate-Mode. Here I'd 
like to cite the help-screen: Do not use options '-F' or '-G' without reading 
the manual first!

By the way, you can mount .dmg images directly to check for your results, 
without having to restore it to a partition first. Most file system repair 
tools will also happily accept an image file. Just make sure you prevent 
writing to your original dmg so you don't compromise the raw rescue result! You 
can work on a copy, write-protect the original (obviously not while ddrescue is 
running), mount with shadow option, use some tool like Disk Arbitrator to 
prevent mounting read-write, or whatever you can think of, but let NO other 
tool except ddrescue write to your image before you have your data safe AND 
know exactly what you are doing. To be clear, that also means DON'T just 
double-click Rescue.dmg without having protected it first!

Good Luck, 
Florian

Am 02.10.2014 um 23:54 schrieb Kevin Doan:

> Dear Sir or Madam,
> 
> After many research I found your great tool on your site and spend =
> several days on trying to recover my damaged external Western Digital =
> hard drive. That being said, it seems like it is taking eternity for it =
> complete therefore I hope if you could help me. I have stopped the =
> process and restarted the PC but speed is still extremely slow.
> 
> GNU ddrescue 1.18.1
> About to copy an unknown number of bytes from /dev/disk3s3 to =
> /Users/kevin/Desktop/Rescue.dmg
>    Starting positions: infile =3D 0 B,  outfile =3D 0 B
>    Copy block size: 4096 sectors       Initial skip size: 128 sectors
> Sector size: 512 Bytes
> 
> Press Ctrl-C to interrupt
> Initial status (read from logfile)
> rescued:     8716 MB,  errsize:   6676 MB,  errors:    2056
> 
> Current status
> rescued:     9177 MB,  errsize:   7092 MB,  current rate:        0 B/s
>   ipos:    77938 MB,   errors:    2142,    average rate:     118 kB/s
>   opos:    77938 MB, run time:    1.07 h,  successful read:      38 s =
> ago
> Copying non-tried blocks... Pass 1 (forwards)
> 
> 
> Even with the incomplete the Rescue.dmg file I tried to use the below =
> command to recover the files:
> 
> kevin$ sudo /opt/local/bin/ddrescue --force -v -c 4096 =
> /Users/kevin/Desktop/Rescue.dmg /dev/rdisk4s2 =
> /Users/kevin/Desktop/MPA/recovery.log
> 
> But without any luck. Any help you could provide is greatly appreciated.
> 
> Thank you and best regards,
> Kevin
> 
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