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https://issues.apache.org/jira/browse/CASSANDRA-7386?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14208141#comment-14208141
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Robert Stupp commented on CASSANDRA-7386:
-----------------------------------------
Not really.
It basically calculates the "value" or a drive using {{free-space-precentage
divided by drive-usage-rate}} (rate is basically the current # of read+write
requests)
which is intended to mean that
* drives with more free space have a higher chance to get new sstables
* drives with low access rate have a higher chance to get new sstables
or vice versa
* "hammered" drives are unlikely to get new data
* full drives are unlikely to get new data
> JBOD threshold to prevent unbalanced disk utilization
> -----------------------------------------------------
>
> Key: CASSANDRA-7386
> URL: https://issues.apache.org/jira/browse/CASSANDRA-7386
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Reporter: Chris Lohfink
> Assignee: Alan Boudreault
> Priority: Minor
> Fix For: 2.1.3
>
> Attachments: 7386-v1.patch, 7386v2.diff, Mappe1.ods,
> mean-writevalue-7disks.png, patch_2_1_branch_proto.diff,
> sstable-count-second-run.png
>
>
> 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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