IBM released version 5.1 of its AIX 5L Unix operating system in June, and will begin shipping server systems built with its new Power 4 processor and the updated software later this year.
AIX 5L was previously known as Project Monterey, and was developed jointly by IBM and the server software division of SCO, now part of Caldera. Caldera's contribution means that for the first time, IBM's Unix operating system can be used with both IBM PowerPC processors and the emerging Intel IA-64 Itanium chips.
The Web-based Smit system management tool has been updated and is now the default method of overseeing the system. It provides a user-friendly interface to the Unix commands, making it easier for novice systems administrators to work without having to remember the complicated syntax for Unix commands and programs.
Workload management
AIX also includes several architectural improvements to support IBM's new Power 4 processor. For example, the Workload Manager (WLM) has been updated. WLM is a long-standing feature of AIX that allows IT managers to isolate applications, so they consume only predetermined amounts of processor, RAM and disk bandwidth.
The new WLM should make it easier to allocate resources to individual Unix applications or groups of applications. This will make AIX and the IBM pSeries more attractive as a platform for the consolidation of several applications onto one server.
However, this feature does not provide the robustness of hardware partitioning, as offered by Sun Microsystems' E10000 and Hewlett-Packard's Superdome Unix servers.
Consolidation projects can also gain a significant advantage from the new logical partitioning (LPAR) support provided by AIX. At the moment, LPAR is a feature of IBM's mainframes that allows those systems to run several operating systems concurrently. The new version of AIX supports the LPAR feature to the extent that AIX can now be run inside an LPAR. IBM is expected to announce new systems later this year that will feature LPAR software and the ability to run several instances of AIX and Linux operating systems.
Software compatibility with the previous version of AIX is less than ideal. While AIX has supported 64bit applications for some time, the previous kernel was designed to use 32bit driver software. The new kernel sacrifices this feature, and as a consequence all 64bit applications written for AIX 4.x need to be recompiled for 5L Â as do all AIX 4.x drivers. This should not be as complicated a process as is required to recompile Windows drivers for Itanium because in IBM's case, the source code does not need to be changed. Some Windows developers must make major modifications before recompiling their code for Itanium.
The other major change in AIX 5L has been to introduce features modelled on the current version of the open Unix specification, SVR4. The printing system in AIX 4.x conformed to an earlier standard, while AIX 5L uses an SVR4-compatible printing subsystem. Such developments may be appreciated by operations staff who are familiar with Solaris or HP-UX, both of which are SVR4-based environments.
IBM has also lifted some of the current limits to scalability. The new Journal File System 2 (JFS2) can accommodate files of up to 2TB in size and has been verified by IBM with a disk volume of four petabytes. Applications that use large amounts of data  notably databases and modelling systems  will benefit most from these changes.
Processor power
Similar headroom has been added to the maximum number of processors, which is now set at 32, and maximum RAM, now set at 256GB. IBM does not currently produce any servers capable of running with more than 24 processors or 96GB RAM. However, following the rule of thumb whereby customers typically configure systems with around one quarter of the maximum possible RAM, the new limits suggests that 64GB RAM configurations will become popular in a year or so.
The maximum complement of processors and RAM supported by AIX and the Power architecture compares well with Itanium-based systems, which have a maximum of four processors and 64GB RAM.
Improvements have also been made to the Reliable Scalable Cluster Technology (RSCT) server management software. Originally developed by IBM to facilitate remote management of its RS/6000 Scalable Parallel (SP) systems, this software has been ported to AIX. Similar in concept to third-party management tools such as Tivoli or CA Unicenter, RSCT provides finer grain inspec-tion and control than more generic tools.
Other changes to the file system improve fault tolerance. The hard disk's logical volume manager (LVM) now has hot-spot management, for example. This feature monitors the utilisation of the hard disks and automatically spreads across all the disks any files that are being used heavily. The idea is to improve performance by making all disks work equally.
Compatibility with Linux and some other versions of Unix has also been improved with the addition of the /proc directory structure, which is populated with entries for all current processes. This should make it easier to port software that was originally written for Linux to the AIX platform. Similarly, AIX now includes the Truss debugger, which is popular with a number of Solaris developers.
