Is there a method of getting a percentage on a DD in linux?

See answers from this question ^[1]

pv

For example you can use pv before you start

sudo apt-get install pv    # if you do not have it
pv < /dev/sda > /dev/sc3   # it is reported to be faster
pv /dev/sda > /dev/sc3     # it seems to have the same speed of the previous one
#or 
sudo dd if=/dev/sda | pv -s 1844G | dd of=/dev/sdc3  # Maybe slower 

Output ^[2]:

440MB 0:00:38 [11.6MB/s] [======>                             ] 21% ETA 0:02:19

^{Notes:
Especially for large files you may want to see man dd and set the options needed to speed up all on your hardware, e.g. bs=100M to set the buffer, oflag=sync to count the effective bytes written, maybe direct...
The option -s only takes integer parameters so 1.8T-->1844G.
As you can notice from the first lines you do not need dd at all.}

kill -USR1 pid

If you already launched the dd command, once you have individuated its PID (Ctrl-Z +bg and you read it , or pgrep ^dd ... ) you may send a signal USR1 (or SIGUSR1, or SIGINFO see below) and read the output.
If the PID of the program is 1234 with

kill -USR1 1234

dd will answer on the terminal of its STDERR with something similar to

4+1 records in
4+0 records out
41943040 bytes (42 MB) copied, 2.90588 s, 14.4 MB/s

^{Warning: Under OpenBSD you may have to check in advance the behaviour of kill[3]: use instead
kill -SIGINFO 1234.
It exists the sigaction named SIGINFO. TheSIGUSR1 one, in this case, should terminate the program (dd)...
Under Ubuntu use -SIGUSR1 (10).}

My go-to tool for this kind of stuff is progress:

This tool can be described as a Tiny, Dirty, Linux-and-OSX-Only C command that looks for coreutils basic commands (cp, mv, dd, tar, gzip/gunzip, cat, etc.) currently running on your system and displays the percentage of copied data. It can also show estimated time and throughput, and provides a "top-like" mode (monitoring).

It simply scans /proc for interesting commands, and then looks at directories fd and fdinfo to find opened files and seek positions, and reports status for the largest file.

It's very light, and compatible with virtually any command.

I find it particularly useful because:

• compared to pv in pipe or dcfldd, I don't have to remember to run a different command when I start the operation, I can monitor stuff after the fact;
• compared to kill -USR1, it works on virtually any command, I don't have to always double-check the manpage to make sure I'm not accidentally killing the copy; also, it's nice that, when invoked without parameters, it shows the progress for any common "data transfer" command currently running, so I don't even have to look up the PID;
• compared to pv -d, again I don't need to look up the PID.

Run dd, then, in a separate shell, invoke the following command:

pv -d $(pidof dd) # root may be required

This will make pv obtain statistics on all the opened file descriptors of the dd process. It will show you both where the read and write buffer sit.

There's an alternative to dd : dcfldd.

dcfldd is an enhanced version of GNU dd with features useful for forensics and security.

Status output - dcfldd can update the user of its progress in terms of the amount of data transferred and how much longer operation will take.

dcfldd if=/dev/zero of=out bs=2G count=1 # test file
dcfldd if=out of=out2 sizeprobe=if
[80% of 2047Mb] 52736 blocks (1648Mb) written. 00:00:01 remaining.

http://dcfldd.sourceforge.net/
https://linux.die.net/man/1/dcfldd

As a percentage you'd have to do some maths, but you can get the progress of a dd in human readable form, even after already starting, by doing kill -USR1 $(pidof dd)

The current dd process will display similar to:

11117279 bytes (11 MB, 11 MiB) copied, 13.715 s, 811 kB/s