nbdkit-rate-filter - limit bandwidth by connection or server
nbdkit --filter=rate PLUGIN [PLUGIN-ARGS...]
[rate=BITSPERSEC]
[connection-rate=BITSPERSEC]
[rate-file=FILENAME]
[connection-rate-file=FILENAME]
[burstiness=SECS]nbdkit-rate-filter is a filter that limits the bandwidth that can be used by the server. Limits can be applied per connection and/or for the server as a whole.
Create a 64M RAM disk and limit server bandwidth as a whole to a maximum of 1 Mbps (megabit per second).
Limit each connection to 50 Kbps (kilobits per second). However as there is no limit to the number of simultaneous connections this does not limit overall server bandwidth.
Limit each connection to 50 Kbps. Additionally the total bandwidth across all connections to the server is limited to 1 Mbps.
Initially limit bandwidth to 1 Mbps. While the server is running the rate can be adjusted dynamically by writing a different rate into /tmp/rate.
Limit each connection to BITSPERSEC.
Limit total bandwidth across all connections to BITSPERSEC.
Adjust the per-connection or total bandwidth dynamically by writing BITSPERSEC into FILENAME. See "DYNAMIC ADJUSTMENT" below.
Control the bucket capacity, expressed as a length of time in "rate-equivalent seconds" that the client is allowed to burst for after a period of inactivity. The default is 2.0 seconds. It's not recommended to set this smaller than the default.
BITSPERSEC can be specified as a simple number, or you can use a number followed by K, M etc to mean kilobits, megabits and so on.
Using the connection-rate-file or rate-file parameters you can dynamically adjust the bandwidth while the server is running.
If the file is not present when the server starts up then the initial rate is taken from the associated connection-rate or rate parameter (or if that is not present, then it is unlimited). If the file is deleted while the server is running then the last rate read from the file continues to be used.
The file should be updated atomically (eg. create a new file, then rename or mv(1) the new file over the old file).
There will be a short delay between the file being updated and the new rate coming into effect.
You can specify rate and connection-rate on their own or together. If you specify neither, the filter is turned off.
The rate filter approximates the bandwidth used by the NBD protocol on the wire. Some operations such as zeroing and trimming are effectively free (because only a tiny NBD message is sent over the network) and so do not count against the bandwidth limit. NBD and TCP protocol overhead is not included, so you may find that other tools such as tc(8) and iptables(8) give more accurate results.
There are separate bandwidth limits for read and write (ie. download and upload to the server).
If the size of requests made by your client is much larger than the rate limit then you can see long, lumpy sleeps in this filter. In the future we may modify the filter to break up large requests automatically in order to limit the length of sleeps. Placing the nbdkit-blocksize-filter(1) in front of this filter, or adjusting burstiness upwards may help.
The filter.
Use nbdkit --dump-config to find the location of $filterdir.
nbdkit-rate-filter first appeared in nbdkit 1.12.
nbdkit(1), nbdkit-blocksize-filter(1), nbdkit-delay-filter(1), nbdkit-exitlast-filter(1), nbdkit-exitwhen-filter(1), nbdkit-limit-filter(1), nbdkit-pause-filter(1), nbdkit-spinning-filter(1), nbdkit-filter(3), iptables(8), tc(8).
Richard W.M. Jones
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