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From "Jonathan Shook (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-10419) Make JBOD compaction and flushing more robust
Date Wed, 30 Sep 2015 03:43:04 GMT
Jonathan Shook created CASSANDRA-10419:
------------------------------------------

             Summary: Make JBOD compaction and flushing more robust
                 Key: CASSANDRA-10419
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-10419
             Project: Cassandra
          Issue Type: Improvement
          Components: Core
            Reporter: Jonathan Shook
         Attachments: timeseries-study-overview-jbods.png

With JBOD and several smaller disks, like SSDs at 1.2 TB or lower, it is possible to run out
of space prematurely. With a sufficient ingestion rate, disk selection logic seems to overselect
on certain JBOD targets. This causes a premature C* shutdown when there is a significant amount
of space left. With DTCS, for example, it should be possible to utilize over 90% of the available
space with certain settings. However in the scenario I tested, only about 50% was utilized,
before a filesystem full error. (see below). It is likely that this is a scheduling challenge
between high rates of ingest and smaller data directories. It would be good to use an anticipatory
model if possible to more carefully select compaction targets according to fill rates.

The attached image shows a test with 12 1.2TB JBOD data directories. At the end, the utilizations
are:
59GiB, 83GiB, 83GiB, 97GiB, 330GiB, 589GiB, 604GiB, 630GiB, 697GiB, 1.055TiB, 1.083TB, 1092TiB,
 



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