more on Symmetrix Archicture

Front End Director
A channel director (front end director) is a card that connects a host to the symmetrix, each card can have upto four ports.
Cache

Symmetrix cache memory buffers I/O transfers between the director channels and the storage devices. The cache is divided up into regions to eliminate contension.
Back End Director

A disk director (back end director) transfers data from disk to cache. Each back-end director can have upto four interfaces (C,D,E and F). Each back-end director interface can handle seven SCSI ids (0-6)

Disk Devices
The disk devices that are attached to the back-end directors could be either SCSI or FC-AL.
Interconnect

The direct matrix interconnect is a matrix of high speed connections to all componentswith bandwidth up to 64Gb/s