Storage Area Networks For Dummies®

Chapter 2: SAN Building Blocks
59
The differences between SAN-enabled
storage arrays
This stuff is really technical, and you don’t need
to know this. If you’re looking to buy a storage
array, though, it might help you figure out what’s
important and what’s not.
Some storage arrays use a data bus architecture,
and others use a data switch architecture
as the internal data paths inside the array itself.
On a bus architecture array, only one thing can
happen at a time per bus. On a switch architecture
array, multiple things can be going on
at the same time. Think of a bus-based array
as being like a narrow road on which only one
car can travel at a time. Think of a switch-based
array as being like a superhighway interchange
where cars can come and go as they please.
The technical term for this is a non-blocking
architecture.
The same holds true for computer networks. A
hub-based network allows only one device at a
time to use the hub; a switched-based network
allows each device to access the switch simultaneously.
A switched-based design is inherently
faster than a bus-based design. The first
of the following two figures shows the slower,
bus-based architecture; the second shows the
faster, switch-based architecture.
Just keep in mind that a switch architecture
can handle many more servers connected to
it without impacting the I/O performance of the
other servers accessing the array. Switches
are inherently more scalable than buses.
Cache
Switch
Cache
Cache
Switch