HP StorageWorks SAN Virtualization Services Platform Best Practices Guide (5697-0935, May 2011)

TIP: When designing a fault-tolerant configuration, be sure to account for a complete fabric
failure. If the failure of one fabric causes the other fabric to become congested, the Quality of
Service (QoS) may be impacted much more than anticipated. Therefore, the fault-tolerant
configuration bandwidth alerts should be reduced to a level so that after a failure, bandwidth
utilization does not exceed 90%. Setting each fabric alert to 45% is a good way to ensure that
the load is balanced and a failure will not prevent the fabric from operating as expected.
SAN switches
All switches on a fabric must be from the same vendor. One fabric can contain switches from one
vendor and the other fabric can have switches from a different vendor. Operating the switches in
vendor neutral roles (or interoperability mode) is not supported for SVSP configurations.
There are two classes of SAN switches: fabric and director. It is better to configure SVSP using
director class switches, which have the ability to expand by adding line cards. This is preferred
over configurations with multiple fabric switches because of the expandability, ease of zoning,
manageability, and performance monitoring capabilities. However, configure director class switches
to ensure that a line card failure does not cause a disruption in the fabric.
Virtual SAN or vSAN from a single switch is not suitable for highly available solutions like SVSP
due to a lack of hardware redundancy. vSAN from a director class switch is supported as long as
hardware redundancy is maintained.
NOTE: Avoid connecting DPMs, VSMs, and arrays to switches where the backplane is
oversubscribed or the number of ports is reduced below a 1:1 ratio. Oversubscription refers to
multiple links funneling into a single link that can result in fabric congestion. These links must be
set up for alarms if the bandwidth exceeds 80%.
Single switch fabric topology
The single and dual switch fabric topologies (director class) do not contain ISLs, thus avoiding any
issues with congested ISLs (see Figure 2 (page 11)). However, this does not ensure that other links
will not become congested, so monitoring and load balancing across multiple paths to the array
is required.
Figure 2 Single switch fabric topology
SAN switches 11