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I work in a local community center as a layman IT-technician where we have to transfer hundreds of GB data every day (documents, audio files, videos and such).

For this purpose, we have a small FreeNAS server (Intel Celeron SoC, 32GB RAM, 3x 8GB ZFS disc array) running on the network with a dedicated backup server.

Unfortunately, some of my colleagues have reported problems transferring larger files to the server storage via SMB. File transfers sometimes fail after a few GB of data and make the FreeNAS server become unavailable to other users for a few seconds. Sometimes, Windows cancels a copy task with an error message, other times the checksums of the local and transferred network files don't match and rarely, the transfer is successful. This also happens when a file is moved from one folder on the server itself to another by a client.

So far, I have only been able to reproduce this issue on Windows 10 machines, our Ubuntu systems have always been able to transfer all files successfully so far, although a bit slower: Ubuntu would move/copy the same file at around 50-60 MiB/s, while Windows 10 will start at around 700, then "crash" and either finish a few seconds later or cancel the transfer with an error).

We've checked all switches, connections and routers for any errors and also revisited the complete network setup in the mean time, but nothing has changed at all regarding this problem. We're certain that this is not a network connection issue, it also affects multiple users routed to the server differently.

The FreeNAS diagnosis logs also look normal, although the interface will crash sometimes directly after a file transfer fails.

Has anybody experienced something similar or could help with the diagnosis of what's the cause for these symptoms? We're at a loss.

  • This one sure smells like network issues. Have you got jumbo frames enabled? Or is your MTU low? Are you tunnelling your network connection anywhere? (VPN, MPLS, anything at all)? – Michael Hampton Dec 14 '18 at 13:48

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