Chapter 6. IBM System x3850 X5 and x3950 X5 245QPI link. If two matched processors of any QPI link speed are installed, this limit is no longeran issue.Of all of the I/O adapters that can be installed on the server, the ServeRAID and 6 Gb SAScontrollers managing SSD drives are the only adapters that can approach the theoreticallimits of the x8 PCIe slot. Therefore, when you use SSD drives, connect no more than eightSSD drives to a single controller for the best performance of the SSD drives. Also, only use x8slots to host the controllers that manage your SSD drives.A single ServeRAID controller managing a single 4-drive SAS HDD array will function withinthe theoretical limits of an x4 PCIe slot. In this case, the mechanical nature of the HDD driveswill limit the maximum throughput of data that passes through the PCIe slot.The dual-port 8 Gbs Fibre Channel, 10Gbs Ethernet, and 10 Gbs Converge Networkadapters (CNA) are all capable of approaching the theoretical limits of an x4 Gen2 PCI slotand might perform better in an X8 Gen2 slot.6.6.3 Cleaning up the boot sequenceOne of the most overlooked steps in completing a hardware setup is deciding from what youare going to boot. The server might have one or more ServeRAID controllers for internaldrives or perhaps another ServeRAID adapter for external drives. You might also be usingone or more Fibre Channel HBAs to access a SAN and you might have Preboot eXecutionEnvironment (PXE) or iSCSI defined to boot to an operating system over the network.By default, your server and the installed options came with the ability to boot from any ofthese sources other than USB storage devices. On every boot, the server is going torecognize each of these boot choices, determine if the bootable media device is attached,and add the optional ROM support to the boot ROM to determine the correct device fromwhich to boot. This process adds time to the boot process.To minimize this loss of time, you can disable the boot options for adapters from which youknow you are never going to boot. The following sections describe common methods ofdisabling boot options.Legacy only modeWhen the server is instructed to boot to Legacy Only mode, the best way to disable unwantedboot sequences is to disable them in F1-Setup by selecting System Settings Device andI/O Ports Enable / Disable Legacy Option ROM(s). Figure 6-20 on page 246 shows theavailable options. You need to know the specific PCIe slots that were used for each adapter,so that you will know which slot to leave enabled.
