[jira] [Created] (CASSANDRA-12619) Improve JBOD throughput

["Natale Galioto (JIRA)" <ji...@apache.org>]

Natale Galioto created CASSANDRA-12619:
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             Summary: Improve JBOD throughput
                 Key: CASSANDRA-12619
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-12619
             Project: Cassandra
          Issue Type: Improvement
            Reporter: Natale Galioto
             Fix For: 3.x


Nodes with spinning disks have very limited throughputs during compactions. This is mainly due to [https://issues.apache.org/jira/browse/CASSANDRA-6696][CASSANDRA-6696] where each SSTable got "sticked" to one data directory only. In order to increase the performance during compactions, reads and writes should always happen on different directories, and a single data directory (for both reads or writes) should be used by no more than one compactor at time. The current throughput of a single spinning disk can get as low as 20MB/s due to r/w seeks penalties, but a compaction between two different spindles could easily get 100MB/s or more throughput. Since 6696 requires sstables to always be on the same data directory, even a compaction between two different data directory and then a "brutal" copy back to the "appropriate" directory could get an overall throughput of 50MB/s. Another option would be to let SStables "float" between two data directories only, and "switch" between them at every compaction.




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