IBM eX5 Implementation Guide

Chapter 6. IBM System x3850 X5 and x3950 X5 239

stand-alone database server with built-in fault tolerance for power and cooling, processors,

memory, and PCIe buses.

6.6.1 Generation 2 and Generation 1 PCIe adapters

All of the PCIe slots in the x3850 X5 are at Generation 2 (Gen 2) specification. Besides

additional error correction and addressing advancements, Gen 2 means that all of the slots of

this server exchange data twice as fast as servers with Gen 1 PCIe slots.

Table 6-6 describes the theoretical limits of each of the common types of PCIe adapters.

Remember that theoretical limits are based on the mathematics of the frequency and data

width of the bits that are transmitted over the interface. Theoretical limits do not include the

necessary communications to maintain the required protocols to interface between intelligent

devices. Theoretical limits also do not consider the inability to maintain a steady flow of data

in full duplex.

Table 6-6 Theoretical data transfer limits of Gen1 PCIe slot types versus Gen2 PCIe slot types

PCIe adapters connect to the processors via the I/O hub. The purpose of the I/O hub is to

combine the various data streams from each of the PCIe slots into a single aggregate link to

the processors using a dedicated QPI link to each processor. The x3850 X5 has two I/O hubs.

The data transfer rate of the QPI link is negotiated between the processor and the I/O hub.

Table 3-9 on page 74 shows the QPI link speeds based on the type of installed processors.

The I/O hub supports the highest QPI link speed that is shown in the table, 6.4 gigatransfers

per second (GT/s). You can also adjust the QPI link speed to conserve power by booting into

F1-Setup, selecting System Settings  Operating Modes, and setting QPI Link Frequency

to values other than the default Max Performance, as shown in Figure 6-15 on page 240.

PCIe adapter/slot type Generation 1 Limit Generation 2 Limit

x1 500 MBs 1 GBs

x4 2 GBs 4 GBs

x8 4 GBs 8 GBs

x16 8 GBs 16 GBs

x32 16 GBs 32 GBs

240 IBM eX5 Implementation Guide

Figure 6-15 QPI Link Frequency setting

PCie adapter compatibility

IBM ServerProven tests IBM and non-IBM adapters that have been proven to function

correctly in the System x3850 X5 server. See the following page for specifics:

http://ibm.com/systems/info/x86servers/serverproven/compat/us/xseries/7148.html

Backward compatibility of Gen2 PCie slots to Gen1 adapters

All Gen2 PCIe slots are backward-compatible to Gen1 adapters; however, not all PCIe

adapter vendors adopted the optional specification of Gen1 that allows a Gen2 PCIe slot to

recognize a Gen1 adapter. When you install a Gen1 PCI adapter that is not recognized by the

server, consider forcing the PCI slot in which the adapter is installed to a Gen1 slot in

F1-Setup by selecting System Settings  Devices and I/O Ports  PCIe Gen1/Gen2

Speed Selection. Figure 6-16 on page 241 shows the resulting panel and the available

selections. The change takes effect after a cold reboot of the server.

Chapter 6. IBM System x3850 X5 and x3950 X5 241

Figure 6-16 PCIe slot speed selection panel to force Gen1 compliance

Non-UEFI adapters in an UEFI environment

A number of Gen1 PCIe adapters were designed prior to the implementation of UEFI. As a

result, these adapters are not recognized or might not have UEFI drivers that allow the

adapter to function in an UEFI environment.

The way that the server supports these non-UEFI adapters is via a setting, Legacy Thunk

Support, which is enabled by default. Legacy Thunk Support mode places the

non-UEFI-aware Gen1 adapter into a generic UEFI wrapper and driver, which allows you to

update the firmware of the adapter to support UEFI.

The recommendation is that all installed adapters either support UEFI as standard or be

updated to support UEFI, because Thunking only provides limited support for non-UEFI

adapters in an UEFI environment. For example, a legacy adapter in a Thunk UEFI wrapper

cannot be seen in System Settings  UEFI Adapters and Device Drivers, nor can it

natively access memory locations above 4 GB.

If you have previously disabled Thunking, you can re-enable it by using F1-Setup and

selecting System Settings  Legacy Support. Figure 6-17 on page 242 shows the Legacy

Support panel.