dev1]$ curl -X PUT -H "Content-Type: application/json" -d '{"props":{"backend":"test"}}' http://127.0.0.1:8098/riak/x124
<html><head><title>500 Internal Server Error</title></head><body><h1>Internal Server Error</h1>The server encountered an error while processing this request:<br><pre>{error,{error,badarg,
              [{erlang,list_to_existing_atom,["backend"]},
               {riak_kv_wm_raw,erlify_bucket_prop,1},
               {lists,map,2},
               {riak_kv_wm_raw,accept_bucket_body,2},
               {webmachine_resource,resource_call,3},
               {webmachine_resource,do,3},
               {webmachine_decision_core,resource_call,1},
               {webmachine_decision_core,accept_helper,0}]}}</pre><P><HR><ADDRESS>mochiweb+webmachine web server</ADDRESS></body></html>

Config file:

%% -*- tab-width: 4;erlang-indent-level: 4;indent-tabs-mode: nil -*-
%% ex: ts=4 sw=4 et
[
 %% Riak Core config
 {riak_core, [
              %% Default location of ringstate
              {ring_state_dir, "data/ring"},

              %% http is a list of IP addresses and TCP ports that the Riak
              %% HTTP interface will bind.
              {http, [ {"127.0.0.1", 8091 } ]},

              %% https is a list of IP addresses and TCP ports that the Riak
              %% HTTPS interface will bind.
              %{https, [{ "127.0.0.1", 8091 }]},

              %% default cert and key locations for https can be overridden
              %% with the ssl config variable
              %{ssl, [
              %       {certfile, "etc/cert.pem"},
              %       {keyfile, "etc/key.pem"}
              %      ]},
              
              %% riak_handoff_port is the TCP port that Riak uses for
              %% intra-cluster data handoff.
              {handoff_port, 8101 },

              %% To encrypt riak_core intra-cluster data handoff traffic,
              %% uncomment the following line and edit its path to an
              %% appropriate certfile and keyfile.  (This example uses a
              %% single file with both items concatenated together.)
              %{handoff_ssl_options, [{certfile, "/tmp/erlserver.pem"}]},

              %% Platform-specific installation paths (substituted by rebar)
              {platform_bin_dir, "./bin"},
              {platform_data_dir, "./data"},
              {platform_etc_dir, "./etc"},
              {platform_lib_dir, "./lib"},
              {platform_log_dir, "./log"}
             ]},

 %% Riak KV config
 {riak_kv, [
            %% Storage_backend specifies the Erlang module defining the storage
            %% mechanism that will be used on this node.
            {storage_backend, riak_kv_multi_backend},
            {multi_backend_default, <<"bitcask">>},
            {multi_backend, [
              {<<"bitcask">>,  riak_kv_bitcask_backend, [
                {data_root, "data/bitcask"}
              ]},
              {<<"test">>, riak_kv_bitcask_backend, [
                {data_root, "data/test"}
              ]}
%             {<<"other">>, riak_kv_bitcask_backend, [
%               {data_root, "data/other"}
%             ]}
            ]},

            %% pb_ip is the IP address that the Riak Protocol Buffers interface
            %% will bind to.  If this is undefined, the interface will not run.
            {pb_ip,   "127.0.0.1" },

            %% pb_port is the TCP port that the Riak Protocol Buffers interface
            %% will bind to
            {pb_port, 8081 },

            %% pb_backlog is the maximum length to which the queue of pending
            %% connections may grow. If set, it must be an integer >= 0.
            %% By default the value is 5. If you anticipate a huge number of
            %% connections being initialised *simultaneously*, set this number
            %% higher.
            %% {pb_backlog, 64},

            %% raw_name is the first part of all URLS used by the Riak raw HTTP
            %% interface.  See riak_web.erl and raw_http_resource.erl for
            %% details.
            %{raw_name, "riak"},

            %% mapred_name is URL used to submit map/reduce requests to Riak.
            {mapred_name, "mapred"},

            %% directory used to store a transient queue for pending
            %% map tasks
            {mapred_queue_dir, "data/mr_queue" },

            %% Each of the following entries control how many Javascript
            %% virtual machines are available for executing map, reduce,
            %% pre- and post-commit hook functions.
            {map_js_vm_count, 8 },
            {reduce_js_vm_count, 6 },
            {hook_js_vm_count, 2 },

            %% Number of items the mapper will fetch in one request.
            %% Larger values can impact read/write performance for
            %% non-MapReduce requests.
            {mapper_batch_size, 5},

            %% js_max_vm_mem is the maximum amount of memory, in megabytes,
            %% allocated to the Javascript VMs. If unset, the default is
            %% 8MB.
            {js_max_vm_mem, 8},

            %% js_thread_stack is the maximum amount of thread stack, in megabyes,
            %% allocate to the Javascript VMs. If unset, the default is 16MB.
            %% NOTE: This is not the same as the C thread stack.
            {js_thread_stack, 16},

            %% Number of objects held in the MapReduce cache. These will be
            %% ejected when the cache runs out of room or the bucket/key
            %% pair for that entry changes
            {map_cache_size, 10000},

            %% js_source_dir should point to a directory containing Javascript
            %% source files which will be loaded by Riak when it initializes
            %% Javascript VMs.
            %{js_source_dir, "/tmp/js_source"},

            %% riak_stat enables the use of the "riak-admin status" command to
            %% retrieve information the Riak node for performance and debugging needs
            {riak_kv_stat, true}
           ]},

 %% Bitcask Config
% {bitcask, [
%             {data_root, "data/bitcask"}
%           ]},

 %% Luwak Config
 {luwak, [
             {enabled, false}
         ]},

%% Riak_err Config
{riak_err, [
            %% Info/error/warning reports larger than this will be considered
            %% too big to be formatted safely with the user-supplied format
            %% string.
            {term_max_size, 65536},

            %% Limit the total size of formatted info/error/warning reports.
            {fmt_max_bytes, 65536}
           ]},        

 %% riak_sysmon config
 {riak_sysmon, [
         %% To disable forwarding events of a particular type, use a
         %% limit of 0.
         {process_limit, 30},
         {port_limit, 30},

         %% Finding reasonable limits for a given workload is a matter
         %% of experimentation.
         {gc_ms_limit, 50},
         {heap_word_limit, 10485760}
        ]},

 %% SASL config
 {sasl, [
         {sasl_error_logger, {file, "log/sasl-error.log"}},
         {errlog_type, error},
         {error_logger_mf_dir, "log/sasl"},      % Log directory
         {error_logger_mf_maxbytes, 10485760},   % 10 MB max file size
         {error_logger_mf_maxfiles, 5}           % 5 files max
        ]}
].