So, per the logs, atleast the writes are bigger now. Can you try adding --debug-fuse & --async-read=false in addition to the same command and try again?
Something like this:
rclone mount ~/Desktop/tmp magnum --volname magnum -o blocksize=1048576 --async-read=false --debug-fuse --log-level=DEBUG --log-file=rclone155beta-local-blocksize.log
hi @ncw,
yes you are right, still 40Mb/s.
I made the test you suggested:
~/ rclone mount ~/Desktop/tmp magnum --volname magnum -o big_writes --log-level=DEBUG --log-file=rclone155beta-local-big_writes.log
and this is the cp:
~/ time cp ~/Desktop/archive.zip magnum/tempAAA
cp ~/Desktop/archive.zip magnum/tempAAA 0.01s user 15.13s system 17% cpu 1:24.84 total
Archive.zip is a 3.1gb (3343531006) and to move it on a differente folder it takes less time:
~/ time cp ~/Desktop/archive.zip ~/Desktop/temporary
cp ~/Desktop/archive.zip ~/Desktop/temporary 0.01s user 1.60s system 56% cpu 2.823 total
Here the logs:
Still no luck.
This is the command:
~/ rclone mount ~/Desktop/tmp magnum --volname magnum -o blocksize=1048576 --async-read=false --debug-fuse --log-level=DEBUG --log-file=rclone155beta-local-debug-fuse.log
The log:
~/ rclone mount ~/Desktop/tmp magnum --volname magnum -o blocksize=1048576 --async-read=false --debug-fuse --log-level=DEBUG --log-file=rclone155beta-local-debug-fuse.log
The error:
Can you try a normal cp once instead?
Looks faster!
Command:
~/ rclone mount ~/Desktop/tmp magnum --volname magnum -o blocksize=1048576 --async-read=false --debug-fuse --log-level=DEBUG --log-file=rclone155beta-local-debug-fuse-with-cp.log
Copy time:
~/ time cp ~/Desktop/archive.zip magnum/tempAAA
cp ~/Desktop/archive.zip magnum/tempAAA 0.01s user 2.97s system 19% cpu 15.475 total
And log:
I am guessing something BlackMagic does while testing doesn't agree with a pre-set block-size since I assume it sets it's own block-size and changes it for the various tests to find the best speeds.
If the cp is working fine, then I think the issue is solved or do you need BlackMagic to work?
Personally, I don't need blackmagic to work. I wanted only to test and see the rclone as a really advantage over monuting the nas on smb 
The topic started for this reason. I'm doing other test that not involve Blackmagic.
I'll use
-o blocksize=1048576 --async-read=false
shall I use also the vfs cache parameter or not?
If you have the space for a local cache, then using full cache-mode is recommended. If not, then not specifying it should also work.
@darthShadow thanks, this is solving for me:
~/ rclone mount magnum:/ magnum --volname magnum --vfs-cache-mode full -o blocksize=1048576 --async-read=false
Using the Finder to move 3.7Gb file I had to try 5 times to get this screenshot:
It was quicker than me 
Amazing!
I'll continue testing and post an update later.
Kudos to you and @ncw for the help and support.
Great.
That was a tricky flag to find since it's not documented anywhere.
And look at this!
~/ rclone mount magnum:/ magnum --volname magnum --vfs-cache-mode full -o blocksize=1048576 --async-read=false --debug-fuse --daemon
Mounting the nas folder, it works also blackmagic with very good speeds!
hi @darthShadow @ncw
after some trial I noticed that the command shared before is not realiable.
Tying to explain some issues:
I moved an empty file of 1MB that I created with this command:
mkfile -n 1m ~/Desktop/TESTFILE
and it this case size is the same (but this file contains just the same characters)
I copied Desktop/archive2.zip (3 343 531 006 bytes) to TMPAAA/archive2 (not the same size 3 343 527 936 bytes) but rclone is not able to sync in on the nas.
If I open the folder over SMB I can see the files being copied, but when the size reaches 200MB fails and restart. It looks like VFS fails the upload .
Before:
After:
Logs:
Are these failures repeatable?
Can you try without "-o blocksize=1048576" and see if you get the failure still? Maybe there is a reason that flag isn't documented...
hi @ncw I see what you mean; I was trying the -o flag because it was suggested in the thread. Without the flag works, but the speed is capped at 40Mb/s.
I currently switched to the stable 1.54 because I need to do some works a need reliability over speed. But I'll testing during this weekend.
If you want me to test something specific or if you want to have a call, I can screenshare live what I'm doing I'm based in south of france (GMT+2)
@ncw looking at new and previous logs I notice this message:
Statfs failed: your remote may not support About: failed to run "df -k /home": Permission denied, please try again.
Is this something that can prevent rclone to get info on my setup for example?
hi,
that problem is documented here
https://rclone.org/sftp/#limitations
"about will fail if it does not have shell access or if df is not in the remote's PATH."