VMware vSphere iSCSI best practices

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　　The following best practices are recommended:
　　· Using iSCSI is worthwhile only if the architecture can take full advantage of this protocol by activating jumbo frames (MTU 9000), which provides excellent performance. This activation must exist from one end of the chain to the other.
　　· Using iSCSI HBA cards becomes essential when using 10-GB connections, and links should be aggregated wherever possible for high performance and redundancy in case of failure.
　　· It is advisable to physically separate the iSCSI storage network from the standard IP network. If this is not possible, streams should be isolated using virtual local-area networks (VLANs).
　　· Use cards with TCP/IP offline engine (TOE) functionality to unload the host from some instructions related to the iSCSI overlay and to reduce the overhead.
　　· Implement quality of service (QoS) by putting the priority on streams. Using vSphere, this can be done using the Storage I/O Control (SIOC) functionality.
　　· Network packet loss is one of the main challenges to achieving good iSCSI network performance. Packet loss can be caused by faulty network configuration or the wrong quality of wiring (for example, using Category 5 cables rather than Category 6 for gigabit links).
　　Note for Jumbo frame:
　　All  devices sitting in the I/O path must be able to implement jumbo frames  for this to provide the full benefits (array controller, physical  switches, network interface cards and VMkernel ports).A common issue  with jumbo-frame configurations is that the MTU value on the switch  isn’t set correctly. In most cases, this must be higher than the hosts  and storage that are typically set to 9,000. Switches must be set higher, for example, to 9,198 or 9,216, to account for IP overhead.