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I created a VM (gen 2). I installed Ubuntu Server 20.04. It is connected to my physical network adapter via External Switch. Then I connect to it with WinSCP to download a 2GB ISO file and it takes ages. I noticed the same behavior when downloading via WinSCP from my Azure server.

The download starts fast, I get like 50MB/s, then it drops to like 100kB/s. Sometimes during the proces I get a higher speed for a while, then it drops again.

Is it WinSCP bug, or what? It's not even a real network connection, it's a transfer between VM and the host, it should be super fast. I can download the ISO over the Internet with a torrent client in 1 minute. The same ISO downloaded from my VM takes over 20 minutes to download.

The VM has 8 cores and 4GB of RAM. My host has 16 cores and 16GB of RAM. I don't even see high resources usage during downloads. My host and VM don't do anything special during downloading the file.

Is there a faster way to transfer files between Ubuntu Server VMs and Windows hosts?

What am I doing wrong?

Harry
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1 Answers1

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The VM and the host are actually using the same hardware, even the same disk if it's the only one you have. This transfer can only be be as fast as a local file copy, with some overhead due to the various virtualization layers involved (*). It definitely will not get any benefit from a faster network connection.

(*) The VM is reading from a virtual disk which is actually a file on the host system, then it's encrypting data and sending it through a virtual network adapter to another virtual network adapter on the host, which will then decrypt the data and write it to the same disk. This can get quite slow.

Massimo
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