Lower speed when writing large files

Copying small files (~10MB) gives a 30MB/s speed
Medium files (~200-300MB) gives a 50MB/s speed
Large files (>1GB) the speed drops to 12MB/s ???
And reading from Ex4 is 100MB/s

These speeds are approximate, sometimes a little better

My 2 Ex4 are raid 10 and connected direct to the PC,
containing 4 red drives 3TB.

No Jumbo MTU, connection cables are original ones.

What can I do for a better speed on GB files writing?

TY in advance

The only chance to speed up is using the IP address instead of the hostname. If you have mounted network shares, unmount them and re-mount by using the ip address, like \\192.168.0.x\Public instead of \\WDMyCloudEX4\Public.

By doing this, you bypass all the DNS requests caused by the SMB or CIFS protocol within your client operating system (I guess it’s Windows). This trick reduced the overhead in network communications, at the end you can make use of more throughput in the network, it will not change anything in bandwidth but reduces the amount of “ping-pong” packet communications.

Thank you for the reply, I checked that.
Each ex4 is on its own subnet with static address.
Also tried smb3 and ftp.

I see a strong activity ~90% cpu on the ex4, the process is smbd.
Maybe large files need more computing power for addressing.

Anyway the ex4 connected to the PC (not on the router) are really fast.