vsphere-esxi-vcenter-server-55-storage-guide

Chapter 14 Best Practices for iSCSI StorageConfiguration changes to avoid this problem involve making sure several input Ethernet links are notfunneled into one output link, resulting in an oversubscribed link. When a number of links transmittingnear capacity are switched to a smaller number of links, oversubscription is a possibility.Generally, applications or systems that write a lot of data to storage, such as data acquisition or transactionlogging systems, should not share Ethernet links to a storage device. These types of applications performbest with multiple connections to storage devices.Multiple Connections from Switch to Storage shows multiple connections from the switch to the storage.Figure 14‐3. Multiple Connections from Switch to Storage1 Gbit1 Gbit1 Gbit1 GbitUsing VLANs or VPNs does not provide a suitable solution to the problem of link oversubscription inshared configurations. VLANs and other virtual partitioning of a network provide a way of logicallydesigning a network, but do not change the physical capabilities of links and trunks between switches.When storage traffic and other network traffic end up sharing physical connections, as they would with aVPN, the possibility for oversubscription and lost packets exists. The same is true of VLANs that shareinterswitch trunks. Performance design for a SANs must take into account the physical limitations of thenetwork, not logical allocations.Checking Ethernet Switch StatisticsMany Ethernet switches provide different methods for monitoring switch health.Switches that have ports operating near maximum throughput much of the time do not provide optimumperformance. If you have ports in your iSCSI SAN running near the maximum, reduce the load. If the port isconnected 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 betweenthese components to handle more load. Ethernet switches also commonly provide information abouttransmission errors, queued packets, and dropped Ethernet packets. If the switch regularly reports any ofthese conditions on ports being used for iSCSI traffic, performance of the iSCSI SAN will be poor.iSCSI SAN Configuration ChecklistThis topic provides a checklist of special setup requirements for different storage systems and ESXi hosts.Table 14‐2. iSCSI SAN Configuration RequirementsComponentAll storage systemsTopologyEMC SymmetrixEMC ClariionHP MSACommentsWrite cache must be disabled if not battery backed.No single failure should cause HBA and SP failover, especially with active-passive storagearrays.Enable the SPC2 and SC3 settings. Contact EMC for the latest settings.Set the EMC Clariion failover mode to 1 or 4. Contact EMC for details.No specific requirementsVMware, Inc. 119