Fibre Channel Protocols - Sun Microsystems StorEdge3000 Series Manual

Direct-Attached Storage (DAS)
Storage Area Network (SAN)
DAS and SAN Storage Architectures
FIGURE 1
Selecting the best storage architecture for a particular environment can be a
confusing exercise. In general, some environments are well-suited for DAS while
others will benefit greatly from SAN.
The challenge of selecting between DAS and SAN is often further complicated by the
need to choose between different storage systems, one designed for DAS or another
intended for SAN. Fortunately, Sun StorEdge 3500 series arrays inherently supports
both DAS and SAN.

Fibre Channel Protocols

The Sun StorEdge 3500 series arrays support point-to-point and Fibre Channel–
Arbitrated Loops (FC–AL) protocols. Using the point-to-point protocol with the Sun
StorEdge 3500 series arrays requires a switched fabric network (SAN), whereas
selecting FC-AL mode enables the arrays to be used in either DAS or SAN
environments. Using point-to-point protocol enables full-duplex use of the available
channel bandwidth, whereas selecting FC-AL mode limits host channels to half-
duplex communication.
In a point-to-point configuration, only one ID can be assigned to each host channel.
If more than one ID is assigned, the point-to-point protocol rules are violated. Any
host channel with more than one ID will not be able to log in to an FC switch in
fabric mode. This "one-ID-per-channel" requirement is true in both single-controller
and dual-controller configurations. Thus, in dual-controller configurations, either the
primary or the secondary controller can have an ID assigned, but not both. This
yields:
6 Sun StorEdge 3000 Family Best Practices Manual • June 2004