Compaq 307560-001 PCI Bus Balancing and Optimization on Compaq ProLiant Server - Page 7

ECG073/0398 WHITE PAPER (cont.) ... PCI BUS LOADING WITH PCI HOT PLUG For servers with PCI Hot Plug slots on a single bus, customers must pay close attention to requirements for availability and determine whether a trade-off is needed between high availability and high performance. Consider the following scenarios: Configuration 1 For high availability and high performance, place the active controllers in the hot-plug slots, with the standby controllers in the non-hot-plug slots. This splits the load so that a single NIC and array controller is on each bus, as shown in Table 3. This configuration provides moderately high availability along with high performance. However since the standby network controller (#4) is in a non-hot-plug slot, if it were to fail replacing the controller would require shutting down the server. The active NIC (#3), on the other hand, is still available and in a hot-plug slot thus allowing the system administrator time to replace the failed NIC (#4) during non-peak hours, when access to the server is at a minimum. This configuration uses the minimum number of PCI hot-plug slots while providing redundancy to controllers. It also enables hot replacement of the primary devices (active) in the event that any of the active controllers should fail. TABLE 3 : HIGH AVAILABILITY AND HIGH PERFORMANCE # Device Type 1 SMART 2/P Drive Array (Active) 2 SMART 2/P Drive Array (Standby) 3 NetFlex-3/P Controller (Active) 4 NetFlex-3/P Controller (Standby) PCI Hot Plug Slot XXXXXX XXXXXX Non-PCI Hot Plug Slot XXXXXX XXXXXX Configuration 2 If high availability is a primary concern, place all four controllers (active and standby) in the hot-plug slots as shown in Table 4. Even though this configuration breaks rule number three in the "Bus Balancing Rules" section, having two network controllers on the same bus does not impact performance since the second NIC is in standby mode and therefore generates minimal traffic on the bus. This configuration works well for high availability because the I/O traffic emitted here is not enough to saturate the PCI bus; therefore, there is no bottleneck to slow I/O traffic. If only two NICs and two drive array controllers are needed, as in Table 4, both drive arrays and network controllers could be placed on same bus without receiving any performance degradation. TABLE 4 : HIGHER AVAILABILITY AND HIGH PERFORMANCE # Device Type 1 SMART 2/P Drive Array (Active) 2 SMART 2/P Drive Array (Standby) 3 NetFlex-3/P Controller (Active) 4 NetFlex-3/P Controller (Standby) PCI Hot Plug Slot XXXXXX XXXXXX XXXXXX XXXXXX Non-PCI Hot Plug Slot 7