Blindly siguiendohttp: //wiki.apache.org/cassandra/CassandraCl, ¿y alguien puede explicar esto?

aaron-mac:apache-cassandra-1.0.0 aaron$ bin/cassandra-cli -host localhost -port 9160
Connected to: "Test Cluster" on localhost/9160
Welcome to the Cassandra CLI.

Type 'help;' or '?' for help.
Type 'quit;' or 'exit;' to quit.

[default@unknown] use Keyspace1;
Authenticated to keyspace: Keyspace1

[default@Keyspace1] create column family User with comparator = UTF8Type; 
5ef4bad0-fb2a-11e0-0000-242d50cf1ffd
Waiting for schema agreement...
... schemas agree across the cluster
[default@Keyspace1] set User['jsmith']['first'] = 'John'; 
org.apache.cassandra.db.marshal.MarshalException: cannot parse 'jsmith' as hex bytes
[default@Keyspace1]