ddrescue on OS X http://superuser.com/q/860067/84988

gpes3e-gjp4:~ gjp22$ date
Sat  3 Jan 2015 00:12:44 GMT
gpes3e-gjp4:~ gjp22$ sudo ddrescue -b 4096 -f -n -v /dev/disk2s2 /dev/disk1s2 /Users/gjp22/Desktop/tall/goodhalf/ddrescue-goodhalf.log
GNU ddrescue 1.19
About to copy an unknown number of Bytes from /dev/disk2s2 to /dev/disk1s2.
    Starting positions: infile = 0 B,  outfile = 0 B
    Copy block size:  16 sectors       Initial skip size: 16 sectors
Sector size: 4096 Bytes

Press Ctrl-C to interrupt
rescued:   501562 MB,  errsize:       0 B,  current rate:    1048 kB/s
   ipos:   501562 MB,   errors:       0,    average rate:    7941 kB/s
   opos:   501562 MB, run time:   17.54 h,  successful read:       0 s ago
Copying non-tried blocks... Pass 1 (forwards)^C
Interrupted by user
gpes3e-gjp4:~ gjp22$ date
Sat  3 Jan 2015 17:45:51 GMT
gpes3e-gjp4:~ gjp22$ sudo ddrescue -b 4096 -c 1Ki -f -n -v /dev/rdisk2s2 /dev/rdisk1s2 /Users/gjp22/Desktop/tall/goodhalf/ddrescue-goodhalf.log
Password:
GNU ddrescue 1.19
About to copy an unknown number of Bytes from /dev/rdisk2s2 to /dev/rdisk1s2.
    Starting positions: infile = 0 B,  outfile = 0 B
    Copy block size: 1024 sectors       Initial skip size: 16 sectors
Sector size: 4096 Bytes

Press Ctrl-C to interrupt
Initial status (read from logfile)
rescued:   501562 MB,  errsize:       0 B,  errors:       0

Current status
rescued:   644429 MB,  errsize:       0 B,  current rate:   12582 kB/s
   ipos:   644429 MB,   errors:       0,    average rate:   19064 kB/s
   opos:   644429 MB, run time:    2.08 h,  successful read:       0 s ago
Copying non-tried blocks... Pass 1 (forwards)^C
Interrupted by user
gpes3e-gjp4:~ gjp22$ sudo ddrescue -b 4096 -c 10Ki -f -n -v /dev/rdisk2s2 /dev/rdisk1s2 /Users/gjp22/Desktop/tall/goodhalf/ddrescue-goodhalf.log
Password:
GNU ddrescue 1.19
About to copy an unknown number of Bytes from /dev/rdisk2s2 to /dev/rdisk1s2.
    Starting positions: infile = 0 B,  outfile = 0 B
    Copy block size: 10240 sectors       Initial skip size: 16 sectors
Sector size: 4096 Bytes

Press Ctrl-C to interrupt
Initial status (read from logfile)
rescued:   644429 MB,  errsize:       0 B,  errors:       0

Current status
rescued:     1492 GB,  errsize:       0 B,  current rate:   20971 kB/s
   ipos:     1492 GB,   errors:       0,    average rate:   19376 kB/s
   opos:     1492 GB, run time:   12.15 h,  successful read:       0 s ago
Copying non-tried blocks... Pass 1 (forwards)