In addition to the parameters used to create a memcached bucket, you can provide replicaNumber to specify the number of replicas for a Couchbase bucket:

shell> curl -u admin:password -d name=newbucket -d ramQuotaMB=20 -d authType=none \
     -d replicaNumber=2 -d proxyPort=11215 http://localhost:8091/pools/default/buckets

POST /pools/default/buckets
HTTP/1.1
Host: node.in.your.cluster:8091
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
Authorization: Basic YWRtaW46YWRtaW4=
Content-Length: xx
name=newbucket&ramQuotaMB=20&authType=none&replicaNumber=2&proxyPort=11215

202: bucket will be created.