I am sure s.t. like this in other threads, but may not be available for s912, anyway it's not in this thread. So if anyone wanted to know the difference between internal memory and SD Card / USB HDD - here some insight:
External helpfull links
HowTo: Linux / UNIX List Just Directories Or Directory Names - nixCraft
https://elinux.org/rpi_sd_cards#sd_card_performance
# SD Card - SanDisk Extreme SDHC UHS-I 32GB class 10 (SDSDX-032G-X46 maybe or s.t. similar)
On Windows with Delink Card Reader I am able to read/write 100/50MB/s, here it changes (and reading is slower - in any test).
(write) LibreELEC:~ # sync; dd if=/dev/zero of=./test.tmp bs=500K count=1024
1024+0 records in
1024+0 records out
524288000 bytes (500.0MB) copied, 15.941096 seconds, 31.4MB/s
(clear) LibreELEC:~ # sync; echo 3 | tee /proc/sys/vm/drop_caches
(read) LibreELEC:~ # sync; time dd if=./test.tmp of=/dev/null bs=500K count=1024
1024+0 records in
1024+0 records out
524288000 bytes (500.0MB) copied, 22.870083 seconds, 21.9MB/s
real 0m 22.87s
user 0m 0.02s
sys 0m 1.32s
# Internal Memory of Beelink GT1-T-D1 3G/32GB/6335/-A (mount -o rw /dev/data /tmp/data)
(write) LibreELEC:~ # sync; dd if=/dev/zero of=/tmp/data/test.tmp bs=500K count=1024
1024+0 records in
1024+0 records out
524288000 bytes (500.0MB) copied, 2.510985 seconds, 199.1MB/s
(clear) LibreELEC:~ # sync; echo 3 | tee /proc/sys/vm/drop_caches
(read) LibreELEC:~ # sync; time dd if=/tmp/data/test.tmp of=/dev/null bs=500K count=1024
1024+0 records in
1024+0 records out
524288000 bytes (500.0MB) copied, 3.693659 seconds, 135.4MB/s
real 0m 3.69s
user 0m 0.01s
sys 0m 1.18s
# USB3.0 HDD Samsung HM750LI (mount -o rw /dev/sda1 /tmp/data)
// Tested on both ports ... ~0,5MB/s difference in 1 Test so .. confirmed and negligible - interesting - 1 port is supposed to be usb 2.0 ... not with that speeds.
(write) LibreELEC:~ # sync; dd if=/dev/zero of=/tmp/data/test.tmp bs=500K count=1024
1024+0 records in
1024+0 records out
524288000 bytes (500.0MB) copied, 9.072689 seconds, 55.1MB/s
(clear) LibreELEC:~ # sync; echo 3 | tee /proc/sys/vm/drop_caches
(read) LibreELEC:~ # sync; time dd if=/tmp/data/test.tmp of=/dev/null bs=500K count=1024
1024+0 records in
1024+0 records out
524288000 bytes (500.0MB) copied, 14.759751 seconds, 33.9MB/s
real 0m 14.76s
user 0m 0.00s
sys 0m 1.07s
(If you do that, don't forget to delete files and unmount)
Short note - over Gbit LAN using Samba (vs. Win10 Client with Intel NIC connected to the HDD) : It's ~ 20MB/s - R/W