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Advanced POWER Virtualization on IBM System p5 - Previous ...

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few cycles to set up, but n<strong>on</strong>e for the actual transfers. Many disks can be mapped<br />

to the same server SCSI adapter without performance degradati<strong>on</strong>.<br />

►<br />

►<br />

For shared processor partiti<strong>on</strong>s, performance will be limited by the partiti<strong>on</strong><br />

definiti<strong>on</strong>s (for example, entitled capacity, and number of processors). Small<br />

partiti<strong>on</strong>s, with respect to small CPU entitlements, communicating with each<br />

other will experience more packet latency due to partiti<strong>on</strong> c<strong>on</strong>text switching.<br />

For dedicated processor partiti<strong>on</strong>s, throughput should be comparable to a<br />

Gigabit Ethernet for small packets, and much better for large packets. For<br />

large packets, the virtual Ethernet communicati<strong>on</strong> is memory-copy-bandwidth<br />

limited.<br />

Tip: In general, high bandwidth applicati<strong>on</strong>s should not be deployed in small<br />

shared processor partiti<strong>on</strong>s. C<strong>on</strong>sider using physical adapters for high<br />

bandwidth applicati<strong>on</strong>s.<br />

Multiple Virtual I/O Servers also present different performance c<strong>on</strong>siderati<strong>on</strong>s,<br />

especially for larger installati<strong>on</strong>s. With many client partiti<strong>on</strong>s using both shared<br />

Ethernet and virtual SCSI, the load <strong>on</strong> the Virtual I/O Server can become<br />

excessive.<br />

Tip: C<strong>on</strong>sider using different Virtual I/O Server to separate competing<br />

workloads, such as network-latency sensitive applicati<strong>on</strong>s and I/O bandwidth<br />

intensive applicati<strong>on</strong>s, and to provide these workloads with guaranteed<br />

resources. In such envir<strong>on</strong>ments, you might c<strong>on</strong>sider separating the virtual<br />

Ethernet from the virtual SCSI and place them in different Virtual I/O Server.<br />

With a Virtual I/O Server dedicated solely to hosting virtual SCSI and another<br />

dedicated solely to Shared Ethernet, the idea of a device driver implementati<strong>on</strong><br />

becomes evident. Keeping redundancy in mind, having a pair of each adds fault<br />

tolerance to the envir<strong>on</strong>ment and keeps the administrati<strong>on</strong> of each Virtual I/O<br />

Server simpler with respect to maintenance.<br />

Separating disk and network traffic<br />

When using MPIO for disk redundancy and SEA Failover for network<br />

redundancy, traffic can be separated to each Virtual I/O Server. In a SEA Failover<br />

c<strong>on</strong>figurati<strong>on</strong>, the network traffic goes through the Virtual I/O Server with the<br />

trunk adapter set to the highest priority (lowest value). AIX 5L MPIO is also for<br />

failover and not load balancing. By default, both paths are set to priority 1 and the<br />

system will select the path to use.<br />

By setting the path priority of MPIO so that disk traffic is directed to the Virtual I/O<br />

Server that is backup for SEA Failover, disk and network traffic are separated.<br />

204 <str<strong>on</strong>g>Advanced</str<strong>on</strong>g> <str<strong>on</strong>g>POWER</str<strong>on</strong>g> <str<strong>on</strong>g>Virtualizati<strong>on</strong></str<strong>on</strong>g> <strong>on</strong> <strong>IBM</strong> <strong>System</strong> <strong>p5</strong>

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