Chris Lohfink created CASSANDRA-7386:
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Summary: JBOD threshold to prevent unbalanced disk utilization
Key: CASSANDRA-7386
URL: https://issues.apache.org/jira/browse/CASSANDRA-7386
Project: Cassandra
Issue Type: Improvement
Reporter: Chris Lohfink
Priority: Minor
Currently the pick the disks are picked first by number of current tasks, then
by free space. This helps with performance but can lead to large differences
in utilization in some (unlikely but possible) scenarios. Ive seen 55% to 10%
and heard reports of 90% to 10% on IRC. With both LCS and STCS (although my
suspicion is that STCS makes it worse since harder to be balanced).
I purpose the algorithm change a little to have some maximum range of
utilization where it will pick by free space over load (acknowledging it can be
slower). So if a disk A is 30% full and disk B is 5% full it will never pick A
over B until it balances out.
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