HP P4000 SAN Technical White Paper page 4

Switch capability
VLAN support
Basic IP routing
Spanning Tree/Rapid
Spanning Tree
Jumbo frame support
4
Description
HP recommends implementing a separate subnet or VLAN for the IP storage network. If you are
implementing VLAN technology within the switch infrastructure, you will typically need to enable
VLAN tagging (802.1q) and/or VLAN trunking (802.1q) or Cisco Inter-Switch Link (ISL). Trunk
aggregation (802.3ad or vendor specific) support is required for full bandwidth. Consult your
switch manufacturer's configuration guidelines when enabling VLAN support.
The storage nodes require access to external services such as DNS, SMTP, SNMP and Syslog. To
support this traffic, you must provide access to these services on your storage network, or provide
routing to external services. In addition, if the storage nodes are to be managed from a remote
network, an IP route must exist to the storage nodes from the management station. Finally, if remote
copy functionality is going to be used, the remote copy traffic must be direct access between the
primary and remote sites.
To build a high availability IP storage network, multiple switches are typically connected into a
single Layer 2 (OSI Model) broadcast domain using multiple interconnects. In order to avoid Layer
2 loops, the Spanning Tree protocol (802.1D) or Rapid Spanning Tree protocol (802.1w) must be
implemented in the switch infrastructure. Failing to do so can cause numerous issues on the IP
storage networks, including performance degradation or even traffic storms.
If supported by the switch infrastructure, HP recommends implementing Rapid Spanning Tree (R-STP)
for faster Spanning Tree convergence. R-STP must be enabled on all ports used for ISLs. All non-ISL
ports should be marked as "edge" ports.
If configured on the switch, disable Spanning Tree on the storage node and server switch ports so
that they do not participate in the Spanning Tree convergence protocol timing.
Large sequential read and write workloads can benefit approximately 10–15% from a larger
Ethernet frame. The storage nodes are capable of frame sizes up to 9 KB. Jumbo frames must be
enabled on the switch, storage nodes, and all servers connected to the HP P4000 SAN. Typically,
jumbo frames are enabled globally or per-VLAN on the switch, and on a per-port basis on the
server. Jumbo frames are enabled individually on each Gigabit NIC in the storage node. Jumbo
frame sizes can be different for each brand. Check your switch documentation on enabling jumbo
frames to determine the proper values taking into account header sizes and padding. It should be
noted that performance could be degraded on certain applications if large frames are enabled.