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When I copy large amounts of data back and forth on my Debian XEN server in the host-VM, the server response in the webserver-VM with nginx becomes very slow.

This is how I cause the problem

  1. in the host VM:

     rsync  -avR /lots/of/files/from/synapse/media_store/ /backup/tmp_matrix_media_store/

  2. in the webserver I monitor the download speed with

    while true; do echo $(date)" - $({ time -p curl -sSf https://test.org?$RANDOM|grep something; } |& grep real)"; done | tee -a /var/log/nginx/performance.log

     Di 23. Mai 09:25:45 UTC 2023 - real 0,73
 Di 23. Mai 09:25:45 UTC 2023 - real 0,20
 ...

I also tried using ionice -c2 -n7 rsync -avR ... to make the copy process less hungry, but this does not help.

Workaround: If I use rsync --bwlimit=10M ... this will slow down the copy progress to max 10 MB/s and and I won't get any problem in the VM.

The server has a CPU : AMD Ryzen 7 3700X Octa-Core with 64GB RAM and the webserver-VM has 4 cores added

What can I do to improve performance?

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2
  • Have you tried ionice -c idle instead of -c2? Commented May 24, 2023 at 9:52
  • Your tests don't do any disk I/O other than those short log entries, right? Commented May 24, 2023 at 9:54

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