Message queues are used to send requests and responses between the Squid and diskd processes.
Shared memory is used for chunks of data to be read and written.
The results are also described here . You need to run Squid version 2.4 or later. Your operating system must support message queues, and shared memory. You didn't put diskd in the list of storeio modules as described above. You need to run configure and and recompile Squid.