IT Management

z990 Opportunities

2 Pages

Based on the continued evolution of the z/OS platform, it is only normal that we expect faster processing speeds, more capacity, and price/performance improvements. The z990 announced in May satisfies these expectations and provides new opportunities. I’ll let IBM and others review the announcements for you; I will focus on two z990 opportunities — consolidation and HiperSockets.


Much has been written about IT consolidation that focuses on the server farm. The z990 presents a good opportunity for the consolidation of z900s and 9672s. In the past, the primary obstacle for consolidating mainframes has been the I/O configuration limit of 255 channels. Each step in mainframe evolution has included one or more of the following: faster engines, more engines, faster interconnections, more interconnections, alternative channel types, etc.

However, few evolutionary steps have included changes in the I/O architecture. The z990 is the exception, as it introduces the concept of Logical Channel Subsystems (LCSSes), which will be available in Oct. 2003.

LCSSes will provide a new level of virtualization in the I/O subsystem. The maximum number of channels for an LCSS is 256, which is the same amount for a z/OS, z/VM, or Linux operating system image. This has not changed. What has changed is that the LPARs do not all have to use the same 256 physical channels. On z990, the LCSS is defined first, and describes which physical channels are in which LCSS. LPARs are defined to a specific LCSS rather than to the physical machine.

LCSSes can share channels between LPARs, and a new capability allows LCSSes to span channels, thus allowing channels to be shared between LCSSes. Figure 1 shows two LCSSes and 30 LPARs, as will be available in Oct. 2003. Note that CHPID FF spans across both LCSSes.

The two LCSSes help greatly when consolidating machines. One machine can be migrated to a new z990 using LCSS 0 while maintaining the 256-channel I/O configuration from the original machine. A second machine can be migrated to the same z990 using LCSS 1. The second machine can then continue to use its same I/O configuration with the 256 channels of LCSS 1. Previously, the two I/O configurations would need to be merged in order to share the 256 channels of an earlier generation mainframe. Merging two I/O configurations can be a very difficult task.


HiperSockets were introduced with z/OS V1R2 in October 2001. Before HiperSockets, LPAR-to-LPAR communication was possible with shared Open Systems Adapters. HiperSockets provided an IP network at memory speeds without physical adapters, often referred to as a Virtual Local Area Network (VLAN). The z900 is limited to four VLANs, but the z990 expands this limit to 16. Channel spanning can be used with HiperSockets. This allows multiple LPARs with different LCSSes access to a single HiperSockets channel.

2 Pages