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https://issues.apache.org/jira/browse/CASSANDRA-2749?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13170364#comment-13170364
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Jonathan Ellis commented on CASSANDRA-2749:
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bq. we cannot stream between two nodes, one using separate cf directory

I don't see any reason to continue to support the old-style directory layout.  
That adds complexity (operationally as well as in the code) for no benefit that 
I can think of.  I think we should migrate from old layout to new on the first 
startup under 1.1.

bq. regarding keyspaces in file names, sure, why not, guess having a header 
with this info in the file is out of the question, then the only meta data we 
have is the file name, right? A problem could be if we want to do 
CASSANDRA-1983 later, that would increase the file name length even more

I'm on the fence here -- on the one hand having ks + cf in the filename 
simplifies some things.  On the other hand, we allow arbitrary-length KS + CF 
names (up to 64K iirc) so UUID aside we're already in trouble on ext3/ext4, 
xfs, and ntfs, which all support max filename length of ~256.  I'm starting to 
think we should move these into the metadata component instead of the filename.
                
> fine-grained control over data directories
> ------------------------------------------
>
>                 Key: CASSANDRA-2749
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-2749
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: Core
>            Reporter: Jonathan Ellis
>            Priority: Minor
>             Fix For: 1.1
>
>         Attachments: 
> 0001-Make-it-possible-to-put-column-families-in-subdirect.patch, 
> 0001-add-new-directory-layout.patch, 
> 0001-non-backwards-compatible-patch-for-2749-putting-cfs-.patch.gz, 
> 0002-fix-unit-tests.patch, 2749.tar.gz, 2749_backwards_compatible_v1.patch, 
> 2749_backwards_compatible_v2.patch, 2749_backwards_compatible_v3.patch, 
> 2749_backwards_compatible_v4.patch, 
> 2749_backwards_compatible_v4_rebase1.patch, 2749_not_backwards.tar.gz, 
> 2749_proper.tar.gz
>
>
> Currently Cassandra supports multiple data directories but no way to control 
> what sstables are placed where. Particularly for systems with mixed SSDs and 
> rotational disks, it would be nice to pin frequently accessed columnfamilies 
> to the SSDs.
> Postgresql does this with tablespaces 
> (http://www.postgresql.org/docs/9.0/static/manage-ag-tablespaces.html) but we 
> should probably avoid using that name because of confusing similarity to 
> "keyspaces."

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