Hi Markus, > "It is generally not recommended to set a replication factor of 3 if > you have fewer than six nodes in a data center". Actually you can create a cluster with 3 nodes and replication level 3. But in this case if one of them would fail cluster become inconsistent. In this way minimum reasonable nodes number is 4 for replication level 3. In this case we can tolerate single node failure. But in this situation each node would contain 3/4 of all data. This is not very good. Number 6 is recommended because in this case each node contain 1/2 of all data, this is quite adequate overhead.
Typically Cassandra clusters don't have big replication level, typically it is 3 (failure of any single node don't crush cluster) or 5 (failure of any two nodes don't crush cluster). For more details you should look to replication level calculator <http://www.ecyrd.com/cassandracalculator/>. -- Thanks, Sergey On 14/04/14 13:25, Markus Jais wrote: > Hello, > > currently reading the "Practical Cassandra". In the section about > replication factors the book says: > > "It is generally not recommended to set a replication factor of 3 if > you have fewer than six nodes in a data center". > > Why is that? What problems would arise if I had a replication factor > of 3 and only 5 nodes? > > Does that mean that for a replication of 4 I would need at least 8 > nodes and for a factor of 5 at least 10 nodes? > > Not saying that I would factor 5 andn 10 nodes, just curious about how > this works. > > All the best, > > Markus
signature.asc
Description: OpenPGP digital signature
