On a sunny day (Wed, 01 Aug 2018 09:53:00 +1200) it happened
nospam.Henri.Derksen@f1208.n280.z2.binkp.net (Henri Derksen) wrote in
:

>Hello Jan,
>
>JP>>> Using external card reader with 2 slots?
>
>HD>> External card reader yes, but NOT using the 2 slots at the same time.
>HD>> The source is the internal SDcard slot: /dev/mmcblk0
>HD>> The destination is /dev/sda
>
>JP> OK, to make a long story short:
>JP> Do Not Do That
>
>JP> When you make copy from a running system to an other card,
>JP> then the source changes while the copy is being made.
>
>Yes I know, but in this case, it does not matter.
>
>JP> Links may be changed, log files may be appended, or created,
>JP> data may be changed.
>
>If you use the machine intensively, yes.
>
>JP> So the new copy will likely not run, and even if it does it WILL contain
>JP> errors and inconsistencies.
>
>Not if you donot use the machine during copying.
>
>JP> The right way is stop the raspi (type poweroff in a terminal perhaps)
>JP> and do the copy on an other system.
>
>Last time I was on a ship with a Pi 2B, only one cardreader and nothing else.
>There were no other machines.
>He was running a corrupted backup from a card his nephew made for him.
>Some people donot shut down the Pi after use ;-(.
>I only had one new fresh filled card with me,
>and he had another card (same type) I made for him in march 2018.
>So I put my new card in the internal slot, and his card from March 2018
>in the cardreader and we made the backup with the internal SDcard copier
>program. This way we always had a working card (from his nephew) if things
went
>wrong. During the backup we did nothing with the machine and it took 90
minutes
>to complete the backup. A long time compared to the 28 minutes I got at my Pi
>3B+ with two cardreaders and dd with 1M blocks.
>I did not expect a three times longer backup time at a Pi 2B versus a 3B+
>But afterwards the new copy worked much better than the crappy backup did.
>
>When sailing and traveling with my foldable bike,
>I do not have enough room to transport a large amount of computer hardware.
>So next time I have to take 2 cardreaders with me, and leave that clean
>underware out of my case ;-).
>I did not use it anyway this time.
>But if I take two cardreaders with me, you should see I only need one,
>and because of an accident (bad meal), I do not have clean underware.
>So it is always trouble to pack the right things when traveling ;-).
>
>Henri.

Yes, that is complicated, you could go naked though, only wear a backpack.
You did say 'you do not use machine during copying'
Linux is very much alive, it is doing things all the time, type
ps avx
to see some processes.
or type
top

That sort of fiddling is not a chance I want to take,
but maybe for an emergency copy..
The other problem you then have is that you cannot run a verify.
diff myimage /dev/sd?
I wrote a special program for that to compare dvd and bluray images, but it
will compare anything:
 http://panteltje.com/panteltje/dvd/dvdimagecmp-0.3.tgz
dvdimagecmp -a /dev/sd? -b myimage.iso
should work
Every disk burn here is compared with it, it gives relative speed compared to
CDs and reports sectors that differ too.

Anyways, for 'on the road' (or in a train) I have a small Asus eeepc that runs
Linux
with a Huawei 3G USB stick to connect to the net, takes hardly any space, and
has a real keyboard.
Usually I just ssh -Y to my home LAN with it, and nobody could tell I was not
there.

Greetings
Jan

--- SoupGate-Win32 v1.05