IBM eX5 Implementation Guide

Chapter 6. IBM System x3850 X5 and x3950 X5 245

QPI link. If two matched processors of any QPI link speed are installed, this limit is no longer

an issue.

Of all of the I/O adapters that can be installed on the server, the ServeRAID and 6 Gb SAS

controllers managing SSD drives are the only adapters that can approach the theoretical

limits of the x8 PCIe slot. Therefore, when you use SSD drives, connect no more than eight

SSD drives to a single controller for the best performance of the SSD drives. Also, only use x8

slots to host the controllers that manage your SSD drives.

A single ServeRAID controller managing a single 4-drive SAS HDD array will function within

the theoretical limits of an x4 PCIe slot. In this case, the mechanical nature of the 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 Network

adapters (CNA) are all capable of approaching the theoretical limits of an x4 Gen2 PCI slot

and might perform better in an X8 Gen2 slot.

6.6.3 Cleaning up the boot sequence

One of the most overlooked steps in completing a hardware setup is deciding from what you

are going to boot. The server might have one or more ServeRAID controllers for internal

drives or perhaps another ServeRAID adapter for external drives. You might also be using

one or more Fibre Channel HBAs to access a SAN and you might have Preboot eXecution

Environment (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 of

these sources other than USB storage devices. On every boot, the server is going to

recognize 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 from

which 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 you

know you are never going to boot. The following sections describe common methods of

disabling boot options.

Legacy only mode

When the server is instructed to boot to Legacy Only mode, the best way to disable unwanted

boot sequences is to disable them in F1-Setup by selecting System Settings  Device and

I/O Ports  Enable / Disable Legacy Option ROM(s). Figure 6-20 on page 246 shows the

available 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.

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Figure 6-20 Legacy option ROM states

When booting from SAN with multiple paths for redundancy, you will need to enable the

legacy option ROM for both HBAs.

The default UEFI mode

On the x3850 X5, you can sequence the order that the UEFI will search the various attached

devices to locate a boot device. You can shorten the time that it takes to perform the search

by moving the adapter that contains the boot device to the top of the list.

In UEFI mode, PXE boot can be disabled for the onboard network interface card (NIC) ports

through F1-Setup by selecting System Settings  Network  PXE Configuration and then

by selecting the port on which you want to disable PXE boot. Figure 6-21 on page 247 shows

the panel that you will see to disable PXE boot on one of the two onboard network ports.

Chapter 6. IBM System x3850 X5 and x3950 X5 247

Figure 6-21 Disabling PXE boot of the onboard network ports

Other PCI adapters can have their boot option ROM disabled from within their configuration

panels. To access individual adapter configuration panels from F1-Setup, select System

Settings  Adapters and UEFI Drivers and press Enter. Figure 6-22 shows the selections

that are presented by this panel when accessed.

Figure 6-22 Accessing adapter-specific configuration information