Re: [Bug-ddrescue] Better alternative switches

[Florian Sedivy]

Hello John, 
looks to me like most you can do is wait …

Just some tips from my experience on OS X:

If the drive still mounts, you should prevent it being mounted read-write or 
being mounted at all. Changes during rescue can potentially invalidate your 
image, and every access on a damaged drive can worsen its state. My favorite 
tool for this is Disk-Arbitrator. 

In my testing, the maximum read speed from a raw /dev/rdisk device was achieved 
using a cluster size of -c 256. This corresponds to 128KiB which is also the 
recommended st_blksize=131072 reported by stat -s /dev/rdisk.. 

If you notice a drop in speed after the first error of a run, you might try 
ddrescue 1.8's new option -O, --reopen-on-error. 

And finally, if you know something about the distribution of your data or of 
the damaged areas on disk, you could experiment with reverse runs or limiting 
the rescue domain. 

Greetings, 
Florian 

Am 09.12.2014 um 09:27 schrieb John:

> ​I have never needed more than a basic invocation of ddrescue to do a
> recovery. That's good but it's also bad since I don't know the tool as well
> as I would like to.
> 
> Generally I have used:
> /ddrescue -v /dev/disk1s3  MyDriveRecovery.dmg MyDriveRecovery.log
> and I have been able to get most stuff back.
> 
> It was suggested I could get stuff off the drive faster if I used the raw
> method so I used:
> 
> mac:ddrescue1.8
> ​me​
> $ sudo ./ddrescue -v /dev/rdisk2s3  /Volumes/My\ Passport\ Air/
> ​Data​
> .dmg
> ​Data​
> .log
> 
> 
> 
> About to copy an undefined number of Bytes from /dev/rdisk2s3 to
> /Volumes/My Passport Air/
> ​Data​
> .dmg
> 
>    Starting positions: infile = 0 B,  outfile = 0 B
> 
>    Copy block size: 128 hard blocks
> 
> Hard block size: 512 bytes
> 
> Max_retries: 0
> 
> Direct: no    Sparse: no    Split: yes    Truncate: no
> 
> 
> Press Ctrl-C to interrupt
> 
> Initial status (read from logfile)
> 
> rescued:    16555 MB,  errsize:    983 GB,  errors:       6
> 
> Current status
> 
> rescued:    18391 MB,  errsize:    981 GB,  current rate:     4608 B/s
> 
>   ipos:    18420 MB,   errors:   28137,    average rate:     5027 B/s
> 
>   opos:    18420 MB
> ​This has been running for almost a week now without much more success. (It
> kicked off with an error at 16.1Gb so I restarted it and it's just been
> running).
> 
> Can anyone suggest a better approach. If I stop ddrescue the drive will
> mount again and I can see a list of folders and the files within. I have
> been looking for a controller card for the drive and have not been able to
> locate one so I am just moving forward but very concerned about data
> integrity by plowing forward. Any suggestions?
> 
> Thanks,
> John
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