[jira] [Commented] (CASSANDRA-7386) JBOD threshold to prevent unbalanced disk utilization

["Yuki Morishita (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-7386?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14050732#comment-14050732 ] 

Yuki Morishita commented on CASSANDRA-7386:
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[~snazy] Can we just calculate ```weightedRate = writeRate + readRate```? Since readRate is incremented through SSTableReader#incrementReadCount which is invoked when actually hiting disk. Otherwise, it is good.

I will find the JBOD configured boxes to see how this performs.

> 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
>            Assignee: Robert Stupp
>            Priority: Minor
>         Attachments: 7386-v1.patch, 7386v2.diff, Mappe1.ods, 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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