322 IBM eX5 Implementation GuideOf all of the I/O adapters that can be installed on the server, the ServeRAID and 6 Gbps SAScontrollers, when managing solid-state drives (SSDs), are the only adapters that canapproach the theoretical limits of the x8 PCIe 2.0 slot. When you use SSD drives, connect nomore than 8 SSD drives to a single controller for the best performance of the SSD drives.Only use x8 slots to host the controllers that manage your SSD drives (that is, not slot 4,because it is an x4 slot).A single ServeRAID controller managing a single 4-drive SAS hard disk drive (HDD) array willfunction within the theoretical limits of an x4 PCIe slot. In this case, the mechanical nature ofthe HDD drives will 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 (CNAs) are all capable of approaching the theoretical limits of an x4 PCIe 2.0 slotand might perform better in an x8 PCIe 2.0 slot.7.5.3 Cleaning up the boot sequenceOne of the most overlooked steps in completing a hardware setup is deciding from what youare going to boot. The x3690 X5 server might have one or more ServeRAID controllers forinternal drives or perhaps another ServeRAID adapter for external drives. You might also useone or more Fibre Channel host bus adapters (HBAs) to access a SAN and you might havePreboot eXecution Environment (PXE) or iSCSI defined to boot to an OS over the network.By default, your server and the installed options came with the ability to boot from any ofthese sources besides USB storage devices. On every boot, the server recognizes each ofthese boot choices, determines if bootable media is attached, and adds the optional ROMsupport to the boot ROM to determine the correct device from which to boot. Checking all ofthese boot choices adds time to the boot process.To minimize this loss of time, you can disable the boot options for adapters that you know youare never going to boot from. The following sections describe the 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 7-19 on page 323 shows theavailable options. You need to know the specific PCIe slots that are used for each adapter sothat you will know which slot to leave enabled.
