> earlier: http://cassandra-user-incubator-apache-org.3065146.n2.nabble.com/how-does-compaction-throughput-kb-per-sec-affect-disk-io-td6831711.html
> might not directly throttle the disk I/O?

Again: Compaction throttling will throttle compaction, which affects
both CPU and I/O for fundamental reasons.

In 1.0 (not earlier) there is throttling of internode streaming, with
similar results.

Without 1.0 it is expected that internode throttling is not throttled.

Also note that compaction and streaming throttling would not
necessarily work well with ionice to begin with; for one thing
depending on situation you may not want to be using the CFQ I/O
scheduler in the kernel to begin with (required for ionice to work);
and for another you may want to throttle the process lower than
available idle I/O bandwidth because of the effects on page cache
eviction.

-- 
/ Peter Schuller (@scode on twitter)

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