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From "Chris Lohfink (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-7386) JBOD threshold to prevent unbalanced disk utilization
Date Thu, 12 Jun 2014 18:01:08 GMT
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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