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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-7386) JBOD threshold to prevent unbalanced disk utilization
Date Fri, 13 Jun 2014 01:41:03 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-7386?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14030152#comment-14030152
] 

Jonathan Ellis commented on CASSANDRA-7386:
-------------------------------------------

bq. IMO it is better to track the load of the disk (similar to Unix system load) and not the
currently active tasks.

That's a good idea.  In fact, we already track reads-per-sstable, so I don't think we'd need
to add any extra metrics to do this.

> 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
>         Attachments: patch_2_1_branch_proto.diff
>
>
> 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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