6.5.1

Table Of Contents
Using VLANs or VPNs does not provide a suitable solution to the problem of link oversubscription in
shared configurations. VLANs and other virtual partitioning of a network provide a way of logically
designing a network. However, they do not change the physical capabilities of links and trunks between
switches. When storage traffic and other network traffic share physical connections, oversubscription and
lost packets might become possible. The same is true of VLANs that share interswitch trunks.
Performance design for a SAN must consider the physical limitations of the network, not logical
allocations.
Checking Ethernet Switch Statistics
Many Ethernet switches provide different methods for monitoring switch health.
Switches that have ports operating near maximum throughput much of the time do not provide optimum
performance. If you have ports in your iSCSI SAN running near the maximum, reduce the load. If the port
is connected to an ESXi system or iSCSI storage, you can reduce the load by using manual load
balancing.
If the port is connected between multiple switches or routers, consider installing additional links between
these components to handle more load. Ethernet switches also commonly provide information about
transmission errors, queued packets, and dropped Ethernet packets. If the switch regularly reports any of
these conditions on ports being used for iSCSI traffic, performance of the iSCSI SAN will be poor.
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