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From "Robert Stupp (JIRA)" <>
Subject [jira] [Updated] (CASSANDRA-7386) JBOD threshold to prevent unbalanced disk utilization
Date Wed, 19 Nov 2014 20:19:36 GMT


Robert Stupp updated CASSANDRA-7386:
    Attachment: 7386-2.1-v5.txt

Patch v5 fixes the junit (only change).

Yeah - that was weird. Intention was to check at least 100 iterations (to see whether it gets
wrong) and at max "some more" iterations to give it a very high chance to succeed.

> JBOD threshold to prevent unbalanced disk utilization
> -----------------------------------------------------
>                 Key: CASSANDRA-7386
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Chris Lohfink
>            Assignee: Robert Stupp
>            Priority: Minor
>             Fix For: 2.1.3
>         Attachments: 7386-2.0-v3.txt, 7386-2.0-v4.txt, 7386-2.0-v5.txt, 7386-2.1-v3.txt,
7386-2.1-v4.txt, 7386-2.1-v5.txt, 7386-v1.patch, 7386v2.diff, Mappe1.ods, mean-writevalue-7disks.png,
patch_2_1_branch_proto.diff, sstable-count-second-run.png, test1_no_patch.jpg, test1_with_patch.jpg,
test2_no_patch.jpg, test2_with_patch.jpg, test3_no_patch.jpg, test3_with_patch.jpg
> 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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