Specifications

DATA CENTER BEST PRACTICES
SAN Design and Best Practices 37 of 84
fig24_SAN_Design
Production Site Back-Up Site
A
FC
FC
FC
FC
B
A
B
Brocade
7800
Storage
Array
Storage
Array
FCIP
Brocade
7800
Brocade
7800
Brocade
7800
WAN
IP Network
Figure 23. Four-box solution connected to production fabrics.
In environments that require production fabric attached channel extenders, it is not best practice to connect
the same channel extender to both “A” and “B” fabrics. The best practice is to have two redundant FC fabrics
in all production environments in which an organization would suffer losses if the SAN were to go down. Even
a momentary outage can “blue screen” or hang servers, causing them to have to be rebooted, which can take
a signicant amount of time in some situations. The division of the “A” and “B” fabrics implies that there is
an air gap between the two autonomous fabrics all the way from the server to the storage array. There are no
physical data links between the two independent fabrics. The servers are equipped with FC software drivers (for
example, Microsoft MPIO, EMC PowerPath) for their HBAs that monitor the individual paths sending data across
all of them. If a path is detected as down, the driver will fail over the trafc to the remaining path(s). This is
best practice for maximum availability. This implies that a single channel extender that must connect via the
production fabric cannot connect to both the “A” and “B” fabrics simultaneously, as shown in Figure 24. If no
Fibre Channel Routing (FCR) is being used, the fabric would merge into one big fabric, which clearly destroys
any notion of an A and B fabric. If FCR is used, the fabrics do not merge; however, there is still a device with a
common Linux kernel attached to both fabrics. This is not acceptable if maximum availability is the goal, and it
is considered a poor practice with high risk. Brocade does not recommend this type of architecture. This type of
architecture, having a common device connected to both the A and B fabrics, is also susceptible to human error,
which can also bring down the entire SAN (meaning both A and B fabrics).
fig25_SAN_Design
Production Site Back-Up Site
A
B
A
B
Storage
Array
Storage
Array
FCIP
Brocade
7800
Brocade
7800
WAN
IP Network
Not Recommended
Poor Practice
FC
FC
FC
FC
Figure 24. Poor practice two-box solution connected to production fabrics.
When connecting channel extenders to production fabrics, each production fabric should be designed using
best practice concepts in a traditional core-edge fashion, with the core tier including either the connections to
standalone channel extenders such as the Brocade 7800 or the FCIP-capable blades, such as the Brocade FX8-
24 Extension Blade. Each channel extender should be connected to a fabric using at least two parallel FC ISLs,
as shown in Figure 23.