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From Jonathan Ellis <>
Subject Re: Cassandra Node Requirements
Date Thu, 25 Aug 2011 02:54:16 GMT
On Wed, Aug 24, 2011 at 1:54 PM, Jacob, Arun <> wrote:
> we need to cap data size at 50% of total node storage capacity for
> compaction

Sort of.  There's some fine print, such as the 50% number is only if
you're manually forcing major compactions, which is not recommended,
but a bigger thing to know is that 1.0 will introduce "leveled
compaction" [1] inspired by leveldb.  The free space requirement will
then be a small number of megabytes.


> SSDs are preferred, but of course  reduce storage capacity
> using standard storage means you bump up your RAM to keep as much in memory
> as possible.

You want to keep "as much in ram as possible" either way; whether you
need SSDs or not depends on whether that's adequate for your "hot"
working set.

> is 8TB (meaning 1.33 actual TB storage/node) a reasonable per node storage
> size for Cassandra?

That's fine, but keep in mind that repairing that much data if you
lose a node could take a while.  Other things being equal, I'd prefer
more nodes with less capacity.

Jonathan Ellis
Project Chair, Apache Cassandra
co-founder of DataStax, the source for professional Cassandra support

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