.Part 1 Architecture HP SAN Design Reference Guide 785351-001

switch automatically reroutes data through an alternate fabric path and there is no interruption in
server I/O activity.
Figure 11 Level 2: single resilient fabric
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Level 3: single resilient fabric with multiple device paths
Level 3 is the same as level 2 but also provides multiple server and storage system paths to the
fabric to increase availability (Figure 12). If a switch, server HBA, or storage system path failure
occurs, data is automatically rerouted through an alternate path and there is no interruption in
server I/O activity.
To take full advantage of this level, HP recommends that you connect each server HBA and each
storage system path to a different switch to increase availability and reduce the potential for an
SPOF. This level provides both fabric resiliency and device path redundancy.
NOTE: Certain operating systems may require the use of fabric zoning to define a minimum of
two zoned paths for each server configured with multiple paths in a single fabric.
Figure 12 Level 3: single resilient fabric with multiple device paths
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Level 4: multiple fabrics and device paths (NSPOF)
Level 4 provides multiple data paths between servers and storage systems, but unlike level 3, the
paths connect to physically separate fabrics (Figure 13). This level ensures the highest availability
with NSPOF protection. If a switch, server HBA, or storage system path failure occurs, data is
automatically rerouted through the alternate fabric and there is no interruption in server I/O activity.
Level 4 minimizes vulnerability to fabric failures (for example, improper switch replacement, incorrect
fabric configuration settings, or a fabric service failure). Level 4 also provides the highest level of
Data availability 39