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From "Natale Galioto (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-12907) Different data directories for SSDs and HDDs at configuration level
Date Thu, 24 Nov 2016 15:28:58 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-12907?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15693538#comment-15693538
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Natale Galioto commented on CASSANDRA-12907:
--------------------------------------------

This is another option, but I was not speaking about mapping an entire CF to a specific disk,
I was speaking about mapping automagically non-data files (that really needs to be fast, such
as partition indexes) of *all* the CFs  to a specific disk, independently on how the user
configures its data directories. 

In my opinion, if an user have an SSD, those files should go there, no matter what, this would
greatly improve the performances. Moreover it seems to me to be true for all the configurations.


>From the user point of view, having granularity with table metadata can be good, but "coupling"
node configuration with keyspace/table configuration doesn't sound very attractive, eg adding
a node with different directory naming convention could be problematic.


> Different data directories for SSDs and HDDs at configuration level
> -------------------------------------------------------------------
>
>                 Key: CASSANDRA-12907
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-12907
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Natale Galioto
>              Labels: performance
>
> Currently, users can speed up some CFs by symlinking its data directory to fast media
such as SSDs. In my opinion, instead, configuration file should allow two different sets of
directory: one dedicated to spindles, one dedicated to SSDs. 
> This would allow a "once and for all mixed SSD & HDD configuration", instead of continuously
symlinking the "right" directory each time a CF is created (due to the name mangling of the
CF directories).
> And this in turn would allow a priori knowledge on disk structures, and would allow to
place indexes of all sort (lookup, partition, etc... everything that is needed to "just" locate
data) on fast SSDs, speeding up ALL the CFs instead of only one, while the HDDs could be used
just for data retrieval and sequential reads. 



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