Cleaning Up The Boot Sequence - IBM System x3850 X5 Implementation Manual

Of all of the I/O adapters that can be installed on the server, the ServeRAID and 6 Gbps SAS
controllers, when managing solid-state drives (SSDs), are the only adapters that can
approach the theoretical limits of the x8 PCIe 2.0 slot. When you use SSD drives, connect no
more 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 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 (CNAs) are all capable of approaching the theoretical limits of an x4 PCIe 2.0 slot
and might perform better in an x8 PCIe 2.0 slot.

7.5.3 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 x3690 X5 server might have one or more ServeRAID controllers for
internal drives or perhaps another ServeRAID adapter for external drives. You might also use
one or more Fibre Channel host bus adapters (HBAs) to access a SAN and you might have
Preboot 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 of
these sources besides USB storage devices. On every boot, the server recognizes each of
these boot choices, determines if bootable media is attached, and adds the optional ROM
support to the boot ROM to determine the correct device from which to boot. Checking all of
these 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 you
are never going to boot from. The following sections describe the common methods of
disabling boot options.
Legacy only mode
When the server is instructed to boot to
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 7-19 on page 323 shows the
available options. You need to know the specific PCIe slots that are used for each adapter so
that you will know which slot to leave enabled.
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Legacy Only
mode, the best way to disable unwanted