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

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.
245
Chapter 6. IBM System x3850 X5 and x3950 X5