IBM eServer Cluster 1600 Managed by PSSP 3.5: What's New

70 IBM ^ Cluster 1600 Managed by PSSP 3.5: What’s New

4.1 64-bit compatibility

The AIX 64-bit kernel is capable of supporting a larger number of processors, I/O

devices, and physical memory (the 32-bit kernel is limited to 96 GB of physical

memory). As the internal data structures of the kernel are now extended from 32

to 64 bits, the kernel is also able to support more resources that are used by

application programs, such as processes, threads, open files, and shared

memory segments. Greater accuracy can also be gained from calculations now

performing arithmetic in 64 bits. Since AIX 5L Version 5.1, the 32-bit and 64-bit

kernels have the same minimum hardware system requirements. These are 64

MB of physical memory, 128 MB of initial paging space, and 536 MB of disk

space to hold the AIX operating system.

Until now, PSSP and all dependent software only operated when used with a

32-bit AIX kernel. PSSP 3.5 has been introduced, and this release has been

enhanced to also operate on a 64-bit kernel. The 64-bit kernel support only exists

on control workstations and nodes that meet the following requirements:

򐂰 Running PSSP 3.5 or later

򐂰 Running AIX 5L Version 5.1 Maintenance Level 3 (IY32749) or later

򐂰 Running the AIX 64-bit kernel on supported 64-bit hardware

Except for Virtual Shared Disk (VSD) and Kernel Low-Level Application

Programming Interface (KLAPI), the kernel extensions and device drivers have

been straight ported to the 64-bit environment, meaning that the new 64-bit

versions return the same results to the userspace code as the 32-bit versions.

During the design of the 64-bit implementation, it was noted that VSD and KLAPI

have additional requirements, because they both make use of kernel addresses

across nodes for direct memory access (DMA) buffers. Therefore, the 64-bit

versions of these must be able to understand 32-bit addresses, and vice versa.

These changes are internal and are transparent to the userspace code.

AIX 5L Version 5.1 installs both the 64- and 32-bit kernels by default. You can

switch between 32 bit and 64 bit on nodes running PSSP 3.5. Switching between

the kernels is simple and consists of changing a few links to point to the kernel

image of choice, rebuilding the boot image, and rebooting the system. The

procedure to change from 32 to 64 bit is detailed in Example 4-1 on page 71.

Chapter 4. Parallel System Support Program 3.5 enhancements 71

Example 4-1 Switching from 32-bit to 64-bit AIX kernel

root $ bootinfo -K

32

root $ ln -sf /usr/lib/boot/unix_64 /unix

root $ ln -sf /usr/lib/boot/unix_64 /usr/lib/boot/unix

root $ bosboot -ad /dev/ipldevice

bosboot: Boot image is 13389 512 byte blocks.

root $ shutdown -Fr

*** System Reboot ***

root $ bootinfo -K

64

The procedure to change from 64- to 32-bit kernels is detailed in Example 4-2.

Example 4-2 Switching from 64-bit to 32-bit AIX kernel

root $ bootinfo -K

64

root $ ln -sf /usr/lib/boot/unix_mp /unix

root $ ln -sf /usr/lib/boot/unix_mp /usr/lib/boot/unix

root $ bosboot -ad /dev/ipldevice

bosboot: Boot image is 13389 512 byte blocks.

root $ shutdown -Fr

*** System Reboot ***

root $ bootinfo -K

32

The commands, shown in Example 4-2, (omitting the shutdown command) can

be placed in the script.cust script to run and change the kernel type before the

first reboot at node installation time. The script will then alter any customized

node from that point onward. However, another reboot is needed.

Note: Some adapters might not be supported under the 64-bit kernel. This

means that you will have missing devices when you switch over to 64-bit

mode. For compatibility tables, see Appendix D, “AIX device drivers reference”

on page 199 and the following Web site:

http://www.ibm.com/servers/aix/os/adapters/51.html

Note: If you switch a node back to 32-bit mode after it is installed with the

64-bit defaults, you will have JFS2 file systems running under a 32-bit kernel.

Although this works, it is not recommended.