This article addresses from a business or management perspective the recurring question, “Why Switched FICON?” With a total of up to 288 FICON Express8 channels supported on a System z196, why not just direct attach the control units? (An article in the October/November issue of z/Journal addressed this question from a technical perspective; you can read this article at http://mainframezone.com/it-management/to-switch-or-not-to-switch-thats-the-question. Some of these reasons tie directly to the technical merits of switched FICON.)

Here we will discuss three areas that can help you achieve benefits by using switched FICON:

• Node Port ID Virtualization (NPIV) for implementations of Linux on System z
• Distance and performance at long distance
• Using a fan-in/fan-out architecture.

NPIV and Linux on System z

IBM has supported Linux on System z mainframes since 1999. However, until IBM announced support of NPIV with Linux on System z in June 2005, the adoption rate of Linux on mainframes was slow. Server consolidation has always been a compelling story, but a parallel story for host connectivity consolidation with full support of security features, such as Logical Unit Number (LUN) masking and zoning, wasn’t there. Today, NPIV is supported on the System z9, z10, z196, and z114. With NPIV support, the server and I/O consolidation is there, and it’s compelling.

IBM undertook a well-publicized project at its internal data centers (Project Big Green) and consolidated 3,900 open systems servers onto 30 System z mainframes running Linux. IBM’s Total Cost of Ownership (TCO) savings, taking into account footprint reductions, power and cooling and management simplification costs, was nearly 80 percent for a five-year period. These types of savings are what have led to 19 percent of new IBM mainframe processor shipments now being used for Linux.

Implementing NPIV requires connectivity from the FICON channel card to a switching device (director or smaller port count switch) that supports NPIV. The FICON channel requires a special microcode load be installed to let it transmit SCSI data payloads and function as an FCP channel for use with NPIV. This basically will allow the FICON channel to function in the same manner as an open systems HBA when connecting to the storage network. NPIV lets the user consolidate up to 255 Linux on System z images (servers) behind each FCP channel and use one port on a channel card and one port on the attached switching device for connecting these virtual servers. Essentially, this facilitates massive consolidation of what had been many Host Bus Adaptors (HBAs), each attached to its own switch port in the Storage Area Network (SAN).

IBM recommends configuring no more than 32 Linux images per FCP channel. Before support of NPIV on System z, this level of I/O consolidation was possible with Linux. However. if the end user had implemented LUN masking and zoning on the open systems servers/SAN/storage before the migration to Linux on System z, they couldn’t do so post-migration until NPIV was supported. 

Adopting a common SAN for distributed/open systems and mainframe (FICON) is another interesting approach. This is more commonly known as Protocol Intermix Mode (PIM). IBM has supported PIM in System z environments since 2003. However, PIM wasn’t rapidly adopted until NPIV implementations for Linux on System z increased after the introduction of System z10 in 2008. At that point, enhanced segregation and security beyond simple zoning was possible via switch partitioning or virtual fabrics and logical switches.

With 19 percent of new mainframes being shipped for use with Linux on System z, we can safely say that, at a minimum, 19 percent of mainframe environments are now running a PIM environment. PIM lets users take advantage of the enhancements made in switching technology, performance, and management. The user can now use PIM, fully populate the latest large port count directors with minimal to no oversubscription, while using management capabilities (such as virtual fabrics/logical switches) to fully isolate open systems ports and FICON ports in the same physical director chassis.

Rather than have more switching platforms partially populated in terms of ports that are dedicated to either open systems or mainframe/FICON, PIM allows for consolidation onto fewer switching devices and better asset utilization. This leads to a lower TCO for the storage network and accommodates a consolidated, simplified cabling infrastructure. The one possible and frequent political argument against PIM in 2011 is the question of who controls the PIM SAN.