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Mainframe Solutions

IBM System z Announcements Encourage Channel Consolidation

by Dr.Steve.Guendert on ‎07-30-2013 04:04 AM (6,779 Views)

On 23 July IBM made a series of hardwareoperating system and software announcements for the zEnterprise platforms.  IBM also announced the eagerly awaited new business class zEnterprise with the zBC12 announcement.  There were several parts of each announcement that pertained to I/O and channel technology. One common denominator of each of these parts was that they 1) encourage a movement towards consolidation of channels on the host, and 2) encourage avoiding direct attached FICON channels and adopting switched FICON architectures.


The first channel subsystem enhancement IBM announced was very big news: IBM announced increased addressing with up to 24k subchannels per channel (port) for the FICON Express features.  To help facilitate growth as well as continuing to enable server consolidation, IBM now supports up to 24k subchannels per FICON Express channel (channel path identifier - CHPID). End users will now be able to define more devices per FICON channel, which includes primary, secondary, and alias devices. The maximum number of subchannels across all device types addressable within an LPAR remains at 63.75k for subchannel set 0 and 64k-1 for subchannel sets 1 and higher. This support is exclusive to the zEC12 and the zBC12 and applies to the FICON Express8S, FICON Express8, and FICON Express4 features when defined as CHPID type FC. This is supported by z/OS , z/VM , and Linux on System z.

The z/OS Version 2 Release 1 announcement stated that IBM zEnterprise EC12 and BC12 (zEC12 and zBC12) servers incorporate improved channel load balancing algorithms, designed to provide more consistent I/O rates across the channel subsystem and help improve I/O response times, even when abnormal conditions occur. In support of this new function, z/OS V2.1 is designed to provide an updated health check based on an I/O rate-based metric, rather than on initial control unit command response time.


Dynamic channel path management (DCM) for FICON channels was originally introduced in z/OS V1.11 with support for a single intermediate FICON switch between the channel and control units. In z/OS V2.1, z/OS is designed to enhance DCM to support FICON channel path connections through two intermediate switches. This is intended to make it easier for you to use a smaller number of channels (channel consolidation) and optic fiber connections for FICON I/O, particularly for multi-site installations. To go along with these improvements in FICON DCM, in z/OS V2.1, a number of usability and performance improvements are provided for the z/OS FICON Discovery and Auto Configuration (zDAC) function. These include improved support for Dynamic Channel Path Management (DCM) for FICON channels, improved processing of device number-constrained configurations and those with constrained unit addresses for specific channels, a new capability to enable you to specify switch and CHPID maps to guide path selection, and improved discovery performance.


The next improvement made with z/OS 2.1 that will help drive channel consolidation is with z High Performance FICON (zHPF). The initial support for System z High-Performance FICON zHPF in z/OS V1.11 was for data sets accessed using the media manager component of DFSMS, including VSAM data sets. z/OS V1.13 added support for QSAM, BSAM, and BPAM and allowed EXCPVR callers to use zHPF channel programs. With z/OS V2.1, EXCP is supported. This function is also available for z/OS V1.12 and V1.13 with the PTF for OA38185. This is intended to provide function that programmers can use to achieve significant I/O performance improvements for programs using EXCP.


The final item I believe merits attention is an IBM Statement of Direction (SOD) pertaining to the removal of FICON Express4 support on System z: The IBM zEnterprise EC12 and the IBM zEnterprise BC12 are planned to be the last System z servers to offer support of the FICON Express4 features. FICON Express4 will not be supported on future System z servers as carry forward on an upgrade. IBM goes on to state that enterprises should continue migrating from the FICON Express4 features to the FICON Express8S features.


Taken separately, each one of these items announced by IBM may not be earth shattering.  When you put them all together, taking into account the earlier zEnterprise I/O enhancements such as the PCIe technology and I/O drawers what do you get? 


More definable addresses per channel, improved FICON DCM, zHPF improvements for additional access methods, better load balancing for channels, and a SOD for the eventual elimination of FICON Express 4 channels.  You can see that IBM is making a very compelling technical case for channel consolidation on the mainframe, both the Enterprise Class machines, and the Business Class Machines. 


Take that one step further and a compelling case is also made for the adoption of fan-in fan-out architectures using FICON switching technology in lieu of direct attached storage for IBM z114 and zBC12 clients.  IBM recently qualified the Brocade 6510 (IBM SAN48B-5) FICON switch for System z environments.  The Brocade 6510 is an ideal FICON switching platform for connectivity with the z114 and zBC12.  Clients with z114 or zBC12 can consolidate onto fewer host FICON channels, use a fan-in fan-out switched architecture, and still achieve their availability requirements for accessing storage devices.  The Brocade 6510 allows them to do this more affordably than buying a FICON director for their connectivity requirements.



Dr. Steve