Duplexed structures
Running some or all of the SCA, lock, and group buffer pool structures in duplex mode is one way to achieve high availability for these structures across many types of failures, including lost connections and damaged structures.
Important: 
Choosing the
default duplexing option of synchronous for the lock structure or SCA can have a significant impact
on performance. You can improve the performance for duplex mode by choosing the asynchronous
duplexing option for the lock structure. 
Choosing the
default duplexing option of synchronous for the lock structure or SCA can have a significant impact
on performance. You can improve the performance for duplex mode by choosing the asynchronous
duplexing option for the lock structure. Important: If you decide to duplex the SCA and lock structure,
you must duplex both structures to achieve the availability benefits.
Duplexing only the SCA or only the lock structure does not provide
any benefit.