[Cassandra Wiki] Update of "CassandraHardware" by JonathanEllis

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The "CassandraHardware" page has been changed by JonathanEllis.
http://wiki.apache.org/cassandra/CassandraHardware?action=diff&rev1=3&rev2=4

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+ === General ===
+ 
+ Cassandra assumes that all nodes have equal capacity.  Violating this assumption will lead to poor performance.  Rather than keeping your hardware price fixed and adding increasingly powerful machines as moore's law kicks in, keep capacity (relatively) fixed and add increasingly inexpensive ones.  (This is easier if you start with relatively powerful machines.)
+ 
  === Memory ===
  The most recently written data resides in memory tables (aka [[MemtableThresholds|memtables]]), but older data that has been flushed to disk can be kept in the OS's file-system cache. In other words, ''the more memory, the better'', with 1GB being the minimum recommended in a virtualized environment.  With dedicated hardware there is no reason to use less than 4GB, and at the high end, you see clusters with 16 or 32 GB.