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dcfldd is an advanced version of dd which is more useful than pv in some situations.

One simple advantage dcfldd has over dd is a progress counter displayed by default, although even with dd you can see progress by pressing ctrl-t. However, if all you need is a progress display, pv is really your best bet.

Another useful advantage dcfldd has is the ability to specify hex and ascii patterns, as well as the output of a command as the source. You may also specify multiple outputs.


Wipe a hard disk

This wipes hard disk /dev/rdisk9 with binary 01010101 pattern.

dcfldd pattern=AAAA of=/dev/rdisk9

Resume wiping a hard disk

You can use seek to skip past the first N blocks on the destination disk. If you have to resume multiple times, perhaps the best option is to use bash's arithmetic expansion to add up the number of blocks written.

$ dcfldd pattern=AAAA of=/dev/rdisk3
3328 blocks (104Mb) written.^C
3466+0 records in
3465+0 records out
$ dcfldd pattern=AAAA of=/dev/rdisk3 seek=3328
2936064 blocks (91752Mb) written.^C
2936132+0 records in
2936131+0 records out
$ dcfldd pattern=AAAA of=/dev/rdisk3 seek=$((3328+2936064))

View progress with pv

pv is useful for seeing the transfer rate of the pipe, which can help diagnose continued success or lack thereof with failing hard disks.

root# dcfldd pattern=AAAA | pv | dcfldd of=/dev/rdisk3 seek=$((4192000+504000+10240000+2936064))
512 blocks (16Mb) written.22.1MiB 0:00:07 [21.7MiB/s] [   <=>
1280 blocks (40Mb) written.43.5MiB 0:00:08 [21.5MiB/s] [    <=>
2304 blocks (72Mb) written.79.4MiB 0:00:09 [35.9MiB/s] [      <=>
3584 blocks (112Mb) written. 114MiB 0:00:10 [35.2MiB/s] [       <=>

See Also