Strange bottleneck on a seafile server

Here’s something rather strange I can’t figure.

I got a Seafile server running on physical hardware that performs really nice when uploading large files through the web frontend. (Ubuntu/Apache)

Then there’s another Seafile server running on a virtual machine. (Debian/Apache). It is a backup for the physical one. Both are installed according to the manual.

I stopped the physical one, rsynced the data directory from the physical one to the virtual one, dumped the databases of the physical one and restored them on the virtual one. After starting the virtual one I edited the URLs in the settings so that they’re correct for the virtual one.

Now comes the strange thing:

  • The web frontend on the virtual server works fine.
  • Downloading files is fast.
  • Uploading smaller files less than 1 MB also works fine.
  • Uploading large files 5 MB or above freezes.

What could be wrong here?