Never mind.. --existing-files
Thanx again to all for the help...
rsync -av does not transfer existing files, if destination has identical data. It is not cp and it should not be used to transfer files to directory, which already has other unrelated data. rsync will allow you to put all your data on target file system. Once you have data there, rename and move operations are relatively inexpensive and fast.
If I could open up an CMD/CONSOLE window directly on the KODI/LE server, I think that would solve my problems.. I could initiate a CP process without using the Windows machine at all...
Is that possible??
ssh connection, start screen, run cp or rsync. Not having direct console on the system was never a problem for penguin types. If stuff is not broken.
cp has -v option to do verbose copy and show some progress. Rsync is still better. If you want more visual tools, "system tools" package has "mc" command too.
Your bottleneck is USB throughput. You might check if your media server got USB3 ports and whether you are not CPU bound during copy. You would get serious speed loss, if you are on USB 2.
ext3/4 file systems can be read on Windows with freely available tools or just by getting cd bootable Linux (system rescue cd/Ubuntu/whatever floats your boat). I don't see if your media server is x86 system or some ARM kit. Live booting other Linux might not be an option.
So how slow are moles in January? How much MB/s speed? (MB=MoleButt..)
He is copying from one local drive to another or to network share. cp -r. So it is zero byte/character per second speed.
If copy goes to network share, then it is Wifi or butt load 
of videos. Moles are sleeping in January. Molasses is not. It is up, running and ready to take over Boston.
LibreELEC:~ # which screen
/storage/.kodi/addons/virtual.system-tools/bin/screen
LibreELEC:~ # which rsync
/storage/.kodi/addons/virtual.network-tools/bin/rsync
LibreELEC:~ #
use rsync -av instead of cp -r. You get far better controls for resuming and status details. See screen manual to avoid having ssh connection open.
rsync -e ssh --rsync-path=/storage/.kodi/addons/virtual.network-tools/bin/rsync -av <source>. root@<libreelec-host>:<dest>
If you want to get real bash on LibreElec, you might have to compile it with some options turned off. In case of Debian /bin/bash at least two linked libraries are not on libreelec. Or configure and build bash with --enable-static-link
Information for others
Board got two SATA slots, M2, M2 wireless, 1GbE network port, PCI-E and two USB headers. Integrated fanless CPU. Should have enough connectors for front USB slots and card reader, if your powersupply has connectors that fit and case got slots for it. USB headers are 2.0. Might need cable adapter if your stuff comes with USB 3.0 19 pin connectors.
LibreElec 9.2.3 install works with SATA SSD. CI22M wireless M2 card recognized. NVME SSD support is not good. Autofs on /var/media is not mounting nvme devices. WD Blue nvme keeps getting switched to D3 power state and failing within minutes after starting to write into it. Attaching drive to other board resets it. Samsung 970 EVO Plus NVME is not recognized by BIOS. Both NVMEs are working on other PCI-E Gen3 board. If you plan on getting similar setup, try using NVME drives compatible with PCI-E Gen2 spec and hope that you have better luck than me. If vendor updates BIOS from F3 to newer version, situation might change.
Went with integrated video (Intel i915 driver) and HDMI. Audio goes to TV over same HDMI cable.
Youtube addon required setting up private keys to work.
