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

Chapter 14 Best Practices for iSCSI StorageBecause each application has different requirements, you can meet these goals by choosing an appropriateRAID group on the storage system. To achieve performance goals, perform the following tasks:• Place each LUN on a RAID group that provides the necessary performance levels. Pay attention to theactivities and resource utilization of other LUNS in the assigned RAID group. A high-performanceRAID group that has too many applications doing I/O to it might not meet performance goals requiredby an application running on the ESXi host.• Provide each server with a sufficient number of network adapters or iSCSI hardware adapters to allowmaximum throughput for all the applications hosted on the server for the peak period. I/O spreadacross multiple ports provides higher throughput and less latency for each application.• To provide redundancy for software iSCSI, make sure the initiator is connected to all network adaptersused for iSCSI connectivity.• When allocating LUNs or RAID groups for ESXi systems, multiple operating systems use and share thatresource. As a result, the performance required from each LUN in the storage subsystem can be muchhigher if you are working with ESXi systems than if you are using physical machines. For example, ifyou expect to run four I/O intensive applications, allocate four times the performance capacity for theESXi LUNs.• When using multiple ESXi systems in conjunction with vCenter Server, the performance needed fromthe storage subsystem increases correspondingly.• The number of outstanding I/Os needed by applications running on an ESXi system should match thenumber of I/Os the SAN can handle.Network PerformanceA typical SAN consists of a collection of computers connected to a collection of storage systems through anetwork of switches. Several computers often access the same storage.Single Ethernet Link Connection to Storage shows several computer systems connected to a storage systemthrough an Ethernet switch. In this configuration, each system is connected through a single Ethernet link tothe switch, which is also connected to the storage system through a single Ethernet link. In mostconfigurations, with modern switches and typical traffic, this is not a problem.Figure 14‐1. Single Ethernet Link Connection to StorageWhen systems read data from storage, the maximum response from the storage is to send enough data to fillthe link between the storage systems and the Ethernet switch. It is unlikely that any single system or virtualmachine gets full use of the network speed, but this situation can be expected when many systems share onestorage device.VMware, Inc. 117