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From aaron morton <aa...@thelastpickle.com>
Subject Re: Tiered compation on two disks
Date Sun, 24 Jun 2012 18:04:53 GMT
> I have a Cassandra installation where we plan to store 1Tb of data, split between two
1Tb disks.
In general it's a good idea to limit the per node storage to 300GB to 400GB. This has more
to do with operational issues that any particular issue with cassandra. However storing a
very large number of keys on a single node can result in high memory usage while the server
is idling, and reduced read performance. 
 
> I know that tiered compaction needs 50% free disk space for worst case situation. 
Not really now days, but it's a good idea to treat 50% as a soft limit. 

> How does this combine with the disk split? 
Whenever a new file is written to disk it will use the data directory with the most space.
In general we recommend using a single data directory. 

Hope that helps. 


-----------------
Aaron Morton
Freelance Developer
@aaronmorton
http://www.thelastpickle.com

On 21/06/2012, at 10:56 PM, Flavio Baronti wrote:

> Hi,
> 
> I have a Cassandra installation where we plan to store 1Tb of data, split between two
1Tb disks.
> Tiered compation should be better suited for our workload (append-only, deletion of old
data, few reads).
> I know that tiered compaction needs 50% free disk space for worst case situation. How
does this combine with the disk split? What happens if I have 500Gb of data in one disk and
500Gb in the other? Won't compaction try to build a single 1Tb file, failing since there are
only 500Gb free on each disk?
> 
> Flavio
> 


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