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Posted to commits@cassandra.apache.org by "Jonathan Ellis (JIRA)" <ji...@apache.org> on 2012/06/14 00:47:42 UTC

[jira] [Commented] (CASSANDRA-4292) Per-disk I/O queues

    [ https://issues.apache.org/jira/browse/CASSANDRA-4292?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13294697#comment-13294697 ] 

Jonathan Ellis commented on CASSANDRA-4292:
-------------------------------------------

We'll also want to "reserve" space for in-progress writes; currently we just use the raw free space as reported by the OS, which means that when disks are close to evenly matched we're highly likely to stack multiple new sstables on the same one instead of spreading them out.
                
> Per-disk I/O queues
> -------------------
>
>                 Key: CASSANDRA-4292
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-4292
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Jonathan Ellis
>            Priority: Minor
>
> As noted in CASSANDRA-809, we have a certain amount of flush (and compaction) threads, which mix and match disk volumes indiscriminately.  It may be worth creating a tight thread -> disk affinity, to prevent unnecessary conflict at that level.
> OTOH as SSDs become more prevalent this becomes a non-issue.  Unclear how much pain this actually causes in practice in the meantime.

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