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From "Jeremiah Jordan (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-7386) JBOD threshold to prevent unbalanced disk utilization
Date Thu, 20 Nov 2014 16:11:35 GMT


Jeremiah Jordan commented on CASSANDRA-7386:

[~aboudreault] the fact that without the patch you crash is what this issue is trying to fix.
So that is a GOOD thing that it happens without, but the patch fixes it.

[~snazy] nothing to change here, and no we do not want to bring back disk reservation, that
only caused problems.

> 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, test_regression_no_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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