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From "Robert Stupp (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (CASSANDRA-7386) JBOD threshold to prevent unbalanced disk utilization
Date Sat, 14 Jun 2014 22:26:01 GMT

     [ https://issues.apache.org/jira/browse/CASSANDRA-7386?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Robert Stupp updated CASSANDRA-7386:
------------------------------------

    Attachment: 7386-v1.patch

Here's an initial draft version that collects metrics on data directories and chooses the
directory to write to on a value calculated from _current task load_ and _free disk ratio_.
It's not finished yet because I still have to think about how to weight _load_ and _free ratio_
- maybe also the "write size", too.

> 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: 7386-v1.patch, 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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