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Posted to user@cassandra.apache.org by Flavio Baronti <f....@list-group.com> on 2012/06/21 12:56:03 UTC
Tiered compation on two disks
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
Re: Tiered compation on two disks
Posted by aaron morton <aa...@thelastpickle.com>.
> 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
>