Answer: A long time. In my case I started at around 7:30PM last night and it’s at 1343GB with another ~700GB to go and it’s almost 8AM the following morning.
So at the moment it’s taken 12+HRs to do ~1.3TB.
The total time was from 7:30PM 12/09/2011 to 2:41 13/02/2011. So a little under 20hrs to do the full image copy of 2TB.
I’m using a Western Digital Elemements 3TB USB2.0 External Hard Drive (Model WDBAAU0030HBK-AESN) and the computer driving it is a recent spec i7 with 8GB RAM. The disk I’m rescuing the data off is a Western Digital Green 2TB WD20EARX (A little problem with a deleted partition).
Here is the command as taken from http://sysblogd.wordpress.com/2008/01/05/data-recovery-with-linux-from-hard-drives-cd-roms-or-dvds/
ddrescue -vr-1 /dev/sdb recovered_data.img ddrescue.log
About to copy 2 TBytes from /dev/sdb to recovered_data.img
Starting positions: infile = 0 B, outfile = 0 B
Copy block size: 128 hard blocks
Hard block size: 512 bytes
Direct: no Sparse: no Split: yes Trecent spec i7 with 8GB RAMruncate: no
Press Ctrl-C to interrupt
Initial status (read from logfile)
rescued: 0 B, errsize: 0 B, errors: 0
Current status
rescued: 1343 GB, errsize: 0 B, current rate: 31916 kB/s
ipos: 1343 GB, errors: 0, average rate: 28251 kB/s
opos: 1343 GB, time from last successful read: 0 s
Copying non-tried blocks...
Serial: WCAWZ0594461
As the guy below pointed out, the time to clone a drive as large as that will probably take a lot more time when damaged. And that is usually the case. For example, I’m currently cloning such a drive and it takes say 12 hours to clone 2GB. At this rate it will take more than a year to clone the whole drive. Cheers!