I have used Raspberry pi 4, 4Gb to plotting my external hard drive, and now it took 25 hours and it got only 5% on plotting (Sycing 160608/198923), what I should do?
I plot with 101.4GiB k=32, 1Tb external hard drive using usb 3.0 port
should I use M.2 Nvme to plotting? 
As you have unfortunately noticed: it is not suitable for plotting, you need a great CPU and a good SSD at minimum to plot seriously. Raspberry Pi is good for harvesting only.
Then can I plot with another PC and get harvest with raspberry pi?
Yes, you can certainly have separate plotting and farming computers. If you haven’t yet read through this I’d highly recommend doing so:
No. Not good for plotting. It is very good for farming though, especially since it has robust USB support. One of the Chia team members told me some guy is farming 16k plots off a single Raspberry Pi 4 
… so that’s kinda badass?
16k plots, 101gb per plot… 1.62 Pb? wow.
I’m going to be that guy, but did you not read any FAQ, Github wiki page…anything anywhere before asking this question?
well, now the next person to google this will get the correct result…
https://www.google.com/search?q=is+raspberry+pi+4+good+for+plotting+chia
Well, we need the forum to get a little more google juice… @dchuk did you sign up for webmaster tools for this site?
I have extensively tested an RPi4 for plotting while farming at the same time over the last months. Works great particularly if you consider slow plotting an advantage and not a disadvantage. It is by far the most efficient way to go about Chia farming. More details can be found here: Farm & Plot at the same time on one RPi
I must say, you are one optimistic person! I mean, being happy, even enthusiastic, about ~1 plot/day is surprising to say the least! That’s only a 10tb disk in about 4 months, after all.
I’m down to ~11-12 plots/day on my daily-use Ryzen setup and feeling I’m in SlowMo mode. Almost reasonable, considering I use it for all kinds of things, but certainly workable over time.
The only question I’d wonder about, is with your Pi doing all that it’s doing, how are your farmer response times, and esp., what about if you should be so lucky to actually pass the filter and win a proof? Would your Pi be able to check the proof before others win it?
Nobody stops you from using multiple RPis to plot more per day if you want to invest more. It will still be the most efficient way to go about things. Also, my horizon is years not months. What is the purpose of buying plotting hardware that one will only use for a few months? Unless one is planning to plot for many years with it, it is a non-optimal capital investment.
At first I had awful harvester times, some even above 28 seconds. But I eventually figured out what the problem was. Now my harvester responds in typically less than 1 second even if it passes the filter and finds a proof or partial if you are with a pool. I have tested it with plotting on and off. The way I have set it up there is no measurable impact of plotting while farming on one RPi. In my ebook I address several points of how to ensure that the harvester is as responsive as possible.