When I pass an rsync command from the destination machine (WDMyCloud NAS), rsyncing causes the raspberry used as source to freeze before finishing first (or maybe sometimes second, I don't know for sure) file transfer (though --dry-run never causes this issue). So I have to unplug and re-plug it each time.
Both directories are mounted as cifs from their local network. Source directory is read-only :
pi@raspberry # sudo mount -t cifs -o ro,username=hello,uid=<hello_uid> //192.168.0.40/some/directory /mnt/source/ root@WDMyCloud # mount.cifs -o iocharset=utf8,username=hello //localhost/some/directory/ /home/root/mnt/destination/
Such a command will freeze raspberry quite fast:
root@WDMyCloud # rsync --delete -rltv --progress -e 'ssh -pPORT' hello@raspberry_ip:/mnt/source/ /home/root/mnt/destination/
Exactly the same issue appears when rsync command is passed from another raspberry (actually on same LAN as previous NAS) used as destination : the (remote) source raspberry freezes. So the failure is not related to a specific machine/rsync implementation, at least not on the destination side. On the other side, when rsync is passed on the source raspberry to (remote) destination machine I never experimented any crashes. Furthermore, apart of this problem I never experimented any crash on this raspberry for years.
Has anybody an idea about what is going on here ?
(The destination NAS machine has a dynamic ip, so I don't connect to it, it maintains a ssh tunnel to raspberry, so raspberry can ssh back. Rsyncing from raspberry to NAS through existing tunnel seems to reduce speed at least 5 times, say 10 times, it is not a good solution. Rsyncing directly from raspberry to NAS should be much faster but I don't like to open a ssh port to a root account, and this NAS does not officially/reliably support user creation. So I pass rsync from destination machine.)