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My scenario:

  • Several rural schools
  • Every school:
    • One linux server
    • Limited bandwidth (shared with all school PCs)
    • Electricity not guaranteed (last to leave the school could cut all electricity)
    • Geographically disperse

I have to backup all school linux servers to a central server.

Method of backup chosen: rsync (minimizes bandwidth usage)

Problem: Backup could degrade the network

First approximation: Using --bwlimit=RATE parameter that limits socket I/O bandwidth. But it's a fixed amount, don't take advantage free network time and stands in the way in crowded network time.

Question: Any way to make rsync to use only spare bandwidth? maybe mark its traffic as low priority somehow?

  • That's another reason why many organisation have a segregated back-up network :) If you're running the actual rsync protocol then some form of QoS on the network layer isn't that difficult. If encapsulating rsync in SSH that might be slightly less trivial. – HBruijn Jan 16 '15 at 11:48
  • A bit lost on QoS. Any hint in how to shape this kind of traffic? – Amanda Jan 16 '15 at 12:02
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    @HBruijn Can't be too difficult. The ssh client can be invoked with ssh -o IPQoS=0 or some other number to chose the QoS to use. – kasperd Jan 16 '15 at 12:28
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Does your network support QoS? If it does you should use the right IP TOS field for rsync traffic. You can use Linux tc command for that.

Also there are standard classification scheme . You can mark rsync traffic for example with 0 and watch the difference.

  • It's not enough to mark only, it should be marked and prioritized. – drookie Jan 16 '15 at 12:42
  • Seems that 0 is for normal traffic (normal as no QoS involved?) and other numbers for higher priority traffic. No lower priority traffic (explicitly) on this table. Will 0 be less than other computer on the LAN traffic? – Amanda Jan 16 '15 at 12:50
  • In theory on Linux system - yes. On other it may depends. You can prioritize traffic on your Linux machines (as say drookie) and it may help you ( but only for outbound traffic ). – user2986553 Jan 16 '15 at 13:14

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